Historically, a register was a sign or chalkboard onto which people would write cash transactions for later bookkeeping, often with chalk. It can also be used to mean a paper register such as one would keep of a check book .
To register a charity means to apply to the government for a non-profit organisation to be officially recognised as such, and thus gain more credibility and possible tax relief.
In trade and commerce, the term register is used in Australia and America as a short form for cash register, a device for tracking retail sales and known to the British as a till. This name came into use because the cash register generally replaced earlier registers in use.
A register is a subset of a language used for a particular purpose or in a particular social setting. For example, the average English speaker will likely adhere more closely to prescribed grammar, pronounce gerunds and presentparticiples with a /N/ sound, and refrain from using the word "ain't" when speaking in a formal setting, but the same person could violate all of those restrictions in an informal setting; these two varieties of speech are separate registers of English.
A register is an outlet for forced air, usually as part of a forced air heating and cooling system.
