c. 1300, "sum, aggregate of a collection," from Anglo-French noumbre, Old French nombre and directly from Latin numerus "a number, quantity," from PIE root *nem- "assign, allot; take."
The meaning "written symbol or figure of arithmetic value" is from late 14c. The meaning "single (numbered) issue of a magazine" is from 1795. The colloquial sense of "a person or thing" is by 1894. The meaning "dialing combination to reach a particular telephone receiver" is from 1879; hence wrong number (1886).
The sense of "musical selection" (1885) is from popular theater programs, where acts were marked by a number. Earlier numbers meant "metrical sound or utterance, measured or harmonic expression" (late 15c.) and, from 1580s, "poetical measure, poetry, verse."
Number one "oneself" is from 1704 (mock-Italian form numero uno attested from 1973); the biblical Book of Numbers (c. 1400, Latin Numeri, Greek Arithmoi) is so called because it begins with a census of the Israelites. Childish slang number one and number two for "urination" and "defecation" attested from 1902. Number cruncher is 1966, of machines; 1971 of persons.
To get or have (someone's) number "have someone figured out" is attested from 1853; to say one's number is up (1806) meaning "one's time has come" is a reference to the numbers on a lottery, draft, etc. The numbers "illegal lottery" is from 1897, American English. Do a number on is by 1969, exact meaning unclear; by the early 1970s it can mean "emotionally manipulate" (1970), "damage or injure" (1975), or "assassinate, kill" (1971).