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 "road" instead.
- UK: pavement: a walkway for pedestrians, especially a sidewalk. Suggest using "walkway" 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: "mech" 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 "mudguards" in the UK.
- UK: mudguards: fenders
- US/CA: Crankset / UK: Chainset (though crankset is also used in the UK)
- UK: Seat Pin (but "seat post" 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: "Pass me the Channellocks."
- 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, "track pump" 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 "jee-lay") These are generally armless.
Accessories
- US: water bottle / UK: bidon (said "bee-don").
Other
- US/CA: public transit / UK: public transport. Suggest using "public transportation".
- US/CA: Yield / UK: Give Way
- US/CA: Flat / UK: Puncture -- In the US "puncture" refers only to tire/tube damage from piercing, such as a nail. In the UK "puncture" is also used for pinch flats, valve failures, etc.