When do you use "swab" and when "mop"?

In my dialect (I am from the US), the only use for "swab" in the "mop" sense is on a ship. It's what you do to the decks.

A mop is a swab, but “mopping” is rarely called “swabbing” outside of a hokey nautical context. In contemporary usage, “swab” is only used like you suggest, and also as a noun, as in the case of cotton swabs.

The only time I've heard or seen 'swab' used to mean the same as mop is in 1600s-set pirate stories when someone has to swab the deck.

You’d use a mop on the floor. You wouldn’t use a swab on the floor - it would take far too long to clean it.

I never use swab in that context. I always use mop. The only time I’ve heard swab used in that context is cartoons making jokes about “swab the poop deck.”

I've never heard anyone use "swab" to refer to the large tool for cleaning. "Swab" is for things with cotton on them for medical uses; "mop" is for the tool with a handle. However, I believe you can call a mop a "swab" in a nautical context? Like, sailors might say that. But this is just according to a dictionary; I've never heard it used. (Although "swab" as a verb I have heard in such a context.)

When on a ship. You "swap the deck(s)". Otherwise, use "mop". Nautical stuff has a lot of it's own special vocabulary, which you will mostly run into in movies and books unless you join the Navy/start working on a ship/take up piracy.

Swab is sometimes used on ships. "Swab the deck." Otherwise it's usually just mop.

Mop is both a noun and a verb. As a noun, it refers to this: [https://m.media-amazon.com/images/I/51t9YPWWylL.\_AC\_UF894,1000\_QL80\_.jpg](https://m.media-amazon.com/images/I/51t9YPWWylL._AC_UF894,1000_QL80_.jpg) This is not a swab. You would never call this a swab. Swab is also both a noun and a verb. As a noun, it usually refers to a cotton swab like this one: [https://cleanroom.contecinc.com/hubfs/Website%20Assets/Product%20Center/Product%20Images/Cleanroom/CONSTIX/Constix%20Cotton%20Swabs\_SC2.jpg](https://cleanroom.contecinc.com/hubfs/Website%20Assets/Product%20Center/Product%20Images/Cleanroom/CONSTIX/Constix%20Cotton%20Swabs_SC2.jpg) This is not a mop. You would never call this a mop. Mop as a verb refers to cleaning a surface using a mop (noun). You would never use the verb swab for this except in the exclusively nautical jargon "swabbing the decks."

Mop only applies to cleaning floors.  Swab applies to a more general bit of cleaning material on a string or stick.  There are cotton swabs that you aren’t supposed to use in your ears. There are gun swabs for cleaning a gun (including cannon).  There are clarinet swabs for cleaning the bore.  “Swab the deck” on old ships wasn’t so much to clean it as it was to make sure that the wooden deck was damp to prevent splinters and fire. 

Swab as a verb meaning 'to clean' is an archaic term that has only persisted through maritime vernacular. https://www.etymonline.com/word/swab The modern medical use as a verb comes from 'cotton swab,' the tool used to collect a sample. Mop has a similar origin, but from Latin rather than Germanic, and has persisted as the word for a large cleaning tool consisting of material attached to the end of a stick while swab came to be used exclusively for the tiny version (cotton swabs.) https://www.etymonline.com/word/mop So a sailor will swab the deck of a ship and a doctor will swab your throat to test for disease. But a maid will mop your floor. It might be useful to think of maritime vernacular as its own specialized dialect of English, much like regional variations of British English and American English, because you'll encounter words used in maritime contexts that mean completely different things outside of a maritime context. There's even a phrase, "talk like a sailor" that refers to using gruff, offensive or confusing language.

As nouns: “swab” typically means a small cotton-tipped rod, used for DNA testing or to clean your ears, or a small wad of cotton gauze or similar. “Mop” refers to a large tool with a sponge or strings on the end, which you get wet and use to wash a floor. As verbs: Essentially, both verbs are *typically* used to refer to the use of the objects described above. Ie to “swab” is to use a swab; to “mop” is to use a mop. But there are other, slightly less common verb uses. As a few people have already mentioned, one specific (and fairly archaic) use of the verb “to swab” means to mop the deck of a ship; you would pretty much always use this verb with “deck” as its direct object (ie “I’m going to swab the deck,” never “I’m going to swab,” even if the context already establishes you’re on a ship). You can also use both words in a kind of generic way to mean “wipe,” typically referring to liquids. You might “mop” sweat off your forehead or water off a table. You might “swab” at a stubborn stain or swab a patch of skin. But all of these uses are not super common and in most cases “wipe” will be the more natural word for cleaning up or applying liquid. The most basic tl;dr: these words do similar things but swab is usually small and mop is usually big

swab for small cleaning objects (gauze pads, ear cleaners, etc), mop for mops.

Only when being corny.

I use mop to clean up a spill, or mess. In general that’s a term used for the floor but it can be used in other contexts. Personally I would use “wipe” for other surfaces like counters. Swab can mean to clean a messy floor in an archaic sense, like on a pirate ship in a movie, but generally in modern terms you “swab” something to carefully isolate a substance from a surface, usually as a medical sample, but also to clean an ear or injury. It is a very medically relevant term but otherwise not used frequently.

Mops are bigger, swabs are smaller.

Personally I would only use "swab" as a synonym for mopping if I was saying "swab the deck" referring to a ship. Seeing as how I am not a sailor nor do i write pirate novels, this does not come up very often for me.

No native English speaker will use ‘swab’ to mean ‘mop’ I can almost guarantee you that. I’d never even heard about saying swab to mean mop.

To my mind, a think of a 'swab' as a wiping motion whereas a 'mop' is more of a soaking up or absorption without the flick aspect of wiping.

I feel like mopping is done to clean, but swabbing the deck they were applying either pitch or an oil coating as waterproofing? I’ve never been a pirate or privateer

So, from my understanding, usually "swab" is for little things (swabbing a cut, swabbing your ears), and "mop" is for larger things (mopping the floor, mopping the wall with paint). There are exceptions, of course, like swabbing the decks, as many others have mentioned. But in general, you can't really go wrong using swab for small and mop for big

On a pirate ship.

Mop is when you clean a floor with a long handled device that has cloth or a sponge at the end. That device is called "a mop." "Mop" is the practically the word that is ever used for that process, and there is no other word commonly used for that process besides "mop." You almost never hear this described as "swabbing" the floor except in some archaic language. You can say "scrub" the floor, but scrubbing usually means that you are cleaning it vigorously with your hands. Also the word "mop" isn't used for any other type of cleaning besides cleaning the floor.