Dictionary of regional vocabulary differences (US vs UK) Given that we appear to be about evenly divided between UK and US folks (and given that "Britain and the United States are two countries divided by a common language"), there should be a dictionary of regional differences in bike terms. The main differences seem to be American English and UK/AU/NZ English.

This was discussed on meta a bit, with some ideas there.

Definitely worth looking at https://cooking.stackexchange.com/questions/784/translating-cooking-terms-between-us-uk-au-ca-nz for ideas how to format well.

I'll make this a community wiki, please simply edit the one answer.
I think we can safely ignore trivial spelling differences like tire/tyre and curb/kerb, and concentrate on differences in terminology that tend to confuse people.
Roads and surfaces

US: pavement: concrete or any hard surface used for vehicles or pedestrians. Suggest using &quot;road&quot; instead.
UK: pavement: a walkway for pedestrians, especially a sidewalk. Suggest using &quot;walkway&quot; instead.
UK: tarmac: road surface, same as US asphalt. (In full, tarmacadam (itself short for tar-bound macadam) but asphalt (bitumen) has replaced tar as a binder.)
US: asphalt: road surface, especially a tar-binder concrete
US: cement: commonly mis-used in US to mean concrete, especially for structures

Components

UK: block, US/rest of world: Cassette, though this is becoming rare.
UK: &quot;mech&quot; short for mechanism, US/Europe/ROW: Derailleur
US/CA: fenders: Devices that fit over the wheels to keep things from splashing onto the rider or the bike, called &quot;mudguards&quot; in the UK.
UK: mudguards: fenders
US/CA: Crankset / UK: Chainset (though crankset is also used in the UK)
UK: Seat Pin (but &quot;seat post&quot; is normal UK usage) / US/CA: Seat Post
Short form for Campagnolo (an Italian component manufacturer); US: Campy, UK: Campag

Tools

US/CA: Wrench / UK: Spanner -- grabs the outside of a bolt head
US Crescent wrench -- Crescent is a branch name, known for adjustable wrench/spanners, but not in the UK.
UK Mole grips/Mole wrench / US Vise-Grips -- Locking pliers (brand names which are used generically, but not across US/UK)
US: Channellocks -- Channellock is a brand best known for their multi-position slip-joint pliers.  Always plural:  &quot;Pass me the Channellocks.&quot;
US: Hex Wrench / Hex Key / Allen Wrench / UK/CA: Allen Key -- a hexagonal tool inserted into a bolt head, often L-shaped
UK: track pump / US: floor pump -- In the US, &quot;track pump&quot; is usually only used for a specific style of pump seen at a track, while in the UK it's commonly used to refer to any kind of floor pump.  In Canada both are commonly used, although floor pump may be more familiar to those new to cycling.

Clothing

US/CA: Spandex = UK: Lycra -- They're different brand-names for the same fibre (elastane)
US: wind vest or vest / UK: gilet (said &quot;jee-lay&quot;)  These are generally armless.

Accessories

US: water bottle / UK: bidon (said &quot;bee-don&quot;).

Other

US/CA: public transit / UK: public transport. Suggest using &quot;public transportation&quot;.
US/CA: Yield / UK: Give Way
US/CA: Flat / UK: Puncture -- In the US &quot;puncture&quot; refers only to tire/tube damage from piercing, such as a nail. In the UK &quot;puncture&quot; is also used for pinch flats, valve failures, etc.