Merriam-Webster Online Dictionary
either (adjective)1.
being the one and the other of two - each flowers blooming on either side of the walk plays either instrument well
2.
being the one or the other of two - take either road
the one or the other - take either of the two routes
- used as a function word before two or more coordinate words, phrases, or clauses joined usually by or to indicate that what immediately follows is the first of two or more alternatives can be used either as a guest room or as an office
1.
- likewise moreover used for emphasis after a negative not smart or handsome either
2.
for that matter - used for emphasis after an alternative following a question or conditional clause especially where negation is implied who answers for the Irish parliament? or army either? Robert Browning
Merriam-Webster Online Thesaurus
either (adverb)in addition to what has been said
SYNONIMS:
additionally, again, also, besides, either, further, furthermore, likewise, moreover, then, too, withal, yet