The  quantifiers either and neither are a kind of determiner . We use them to talk about possible choices between two  people or things.

When used as a determiner, either and neither must come before a singular countable noun.

either

Either is positive (+). It means "one OR the other" (of two).

  • A. Do you want to meet on Monday or Tuesday?
    B. Either  day is good for me. (Monday is good for me. Tuesday is good for me.)
  • A. There are two keys here. Which will open the office?
    B. I believe either  key works.

neither

Neither is negative (-). It means "not one AND not the other" (of two).

  • Neither  team scored and the game was a draw. (Team A didn't score. Team B didn't score.)
  • Neither  player was allowed to return to the game after the argument.
We can pronounce each of the words either and neither  in two different ways:
either:  /'i:ðə/ OR /'ʌɪðə/
neither: /'ni:ðə/ OR /'nʌɪðə/

Either pronunciation is acceptable. Neither pronunciation is wrong.

sources : Original Link