early 14c., avantage , "position of being in advance of another," from Old French avantage "advantage, profit, superiority," from avant "before," probably via an unrecorded Late Latin *abantaticum , from Latin abante (see advance ).
The -d- is a 16c. intrusion on the analogy of Latin ad- words. Meaning "a favoring circumstance" (the opposite of disadvantage ) is from late 15c. Tennis score sense is from 1640s, first recorded in writings of John Milton, of all people. Phrase to take advantage of is first attested late 14c.