(Tire valves) A valve stem is a self-contained valve which opens to admit gas to a chamber (such as air to inflate a tire), and is then automatically closed and kept sealed by the pressure in the chamber, or a spring, or both, to prevent the gas from escaping.
The fitting in the valve stem of the wheel that allows you to inflate or deflate the tire.
A bicycle or motorcycle
bicycle: a wheeled vehicle that has two wheels and is moved by foot pedals
motorcycle: a motor vehicle with two wheels and a strong frame
bicycle: ride a bicycle
Capital letters
(cap) a top (as for a bottle)
(cap) a tight-fitting headdress
(cap) lie at the top of; "Snow capped the mountains"
Urban singlespeed
Made from old parts: 1993 frame, DIY chain tensioner, 42x20 transmission, flower lacing pattern on the front, long-arm LX cantilevers with red KoolStop pads, early 90s Flite saddle and John Tomac ODI grips, 1994 Specialized cranks, rear wheel and tires from flea-market bike, handlebar from the junk box at the LBS, custom DIY valve caps.
Matching(ish)
These wheels used to have red Specialized valve caps, which kind of matched the anodized red spoke nipples, but not the rest of the bike. However I went riding today with someone who had a shiny new red, white and black Cube but yellow Continental valve caps. We did the obvious thing and had a multicolour swapshop