Abarim Publications' online Biblical Greek Dictionary
The preposition αντι (anti) expresses substituting, or replacing one thing with another. As such it may be translated with "instead" (James 4:15), "instead of" (Luke 11:11) or even "for/upon" (as in "grace for/upon grace"; John 1:16, or "a coin for you and Me"; Matthew 17:27, or "evil for evil", Romans 12:17).
Since substitution is the basis of economy, our word is also used to describe barter or the exchange of goods for money (Hebrews 12:16). It also frequently describes the exchange of a motivation or circumstance for actual action, in which case it can usually be translated as "because of" or "on account of" (Luke 12:3, Ephesians 5:31).
In compound words, the prefix αντι (anti-) emphasizes otherness and particularly previousness (as in our words "antique" and "antipasto") and substitution (as in the familiar term Antichrist).
Secondarily our prefix reflects opposition or contrariness (as in the verb αντιλεγω, antilego, to speak against). But may just as well describe a formal and proper substitution (as in the word ανθυπατος, meaning proconsul, a deputy governor who acted in the stead of a consul).
Our prefix features in a vast list of compound words, but a true derivation is the adverb αντικρυ (antikru), meaning opposite to or over against (Acts 20:15 only).