Concise Bible Dictionary:
This term occurs only in 1 John 2:20, though the same word, χρίδμα, is twice translated “anointing” in 1 John 2:27. The Holy Spirit is an unction that permeates, as it were, the whole being of the Christian to give him Christ's character.
Strong’s Dictionary of Greek Words:
Meaning:
from 5548; an unguent or smearing, i.e. (figuratively) the special endowment ("chrism") of the Holy Spirit
KJV Usage:
anointing, unction