Bible Dictionaries
Either

Vine's Expository Dictionary of NT Words

is a disjunctive particle. One of its uses is to distinguish things which exclude each other, or one of which can take the place of another. It is translated "either" in Matthew 6:24; 12:33; Luke 16:13; Acts 17:21; 1 Corinthians 14:6 . The RV rightly omits it in Luke 6:42 , and translates it by "or" in Luke 15:8; Philippians 3:12; James 3:12 .

Note: The adverb enteuthen, denoting "hence," is repeated in the phrase rendered "on either side," (lit., "hence and hence") in John 19:18 . The RV of Revelation 22:2 translates it "on this side," distinguishing it from ekeithen, "on that side;" the AV, following another reading for the latter adverb, has "on either side." See HENCE.