nor

Từ điển American Heritage Dictionary 4th

I. nor¹ (nôr; nər when unstressed)conj.
And not; or not; not either:
has neither phoned nor written us; life forms that are neither plants nor animals. [Middle English : ne, no; see no¹ + or, or; see or¹.] 
Usage Note: When using neither in a balanced construction that negates two parts of a sentence, nor (not or) must be used in the second clause: She is neither able nor (not or) willing to go. Similarly, when negating the second of two negative independent clauses, nor (not or) must be used: He cannot find anyone now, nor does he expect to find anyone in the future; Jane will never compromise with Bill, nor will Bill compromise with Jane. Note that in these constructions, nor causes an inversion of the auxiliary verb and the subject (does he... will Bill...). However, when a verb is negated by not or never, and is followed by a verb phrase that is also to be negated (but not an entire clause), either or or nor can be used: He will not permit the change, or (or nor) even consider it. In noun phrases of the type no this or that, or is actually more common than nor: He has no experience or interest (less frequently nor interest) in chemistry. Or is also more common than nor when such a noun phrase, adjective phrase, or adverb phrase is introduced by not: He is not a philosopher or a statesman. They were not rich or happy. See Usage Note at neither. See Usage Note at or¹. II. nor² (nôr, nər when unstressed)conj. Chiefly Southern & Midland U.S.
Than. [Middle English, perhaps ultimately from nor, nor. See nor¹.]