Abarim Publications' online Biblical Greek Dictionary
The familiar correlative pronoun (which is technically an adjective) ετερος (heteros) means other or another, but in the sense of "one of another kind" or "one of another personality". One of the same kind would be described by the also familiar adjective αλλος (allos), and one with which one is one (a same one, or one with whom one is joint) is described by ομος (homos).
English makes no or little distinction between ετερος (heteros) and αλλος (allos) and translates both with "other", and although there is some overlap, in Greek these differences can be profound.
The two masters Jesus mentions in Matthew 6:24 are not simply two similar masters but rather two different kinds of masters, who thus demand whole different kinds of service. And the disciples of John who asked Jesus whether he was the One likewise didn't ask whether another similar One might come but a whole different one (Matthew 11:3). Rather mysteriously, after his resurrection Jesus appeared to Mary Magdalene in one form and to the travelers to Emmaus in whole other sort of form (Mark 16:12).
Our pronoun is used 99 times, see full concordance, and from it derive:
- Together with the noun γλωσσα (glossa), meaning tongue or language: the adjective ετερογλωσσος (heteroglossos), meaning of another language (1 Corinthians 14:21 only).
- Together with the noun διδασκαλος (didaskalos), meaning teacher: the verb ετεροδιδασκαλεω (heterodidaskaleo), meaning "to teach something else" (1 Timothy 1:3 and 6:3 only)
- The adverb ετερως (heteros), meaning differently (Philippians 3:15 only).
- Together with the interrogative pronoun ποιος (poios), meaning what, which, what kind, what sort?: the interrogative pronoun ποτερος (poteros), meaning "which of the two" or simply: whether [this or that]. It occurs in John 7:17 only.