Webster's Revised Unabridged Dictionary · 1913

Vantage

Vantage (vȧn"taj; 48) , noun

[Aphetic form of Old English avantage, from French avantage. See Advantage.]

1.
Superior or more favorable situation or opportunity; gain; profit; advantage. [Rare]
O happy vantage of a kneeling knee! — Shakespeare
2.
A position offering a superior view of a scene or situation; -- used literally and figuratively; as, from the vantage of hindsight; also called vantage point.
3.
(Tennis) The first point scored after deuce; advantage{5}. [British]
It is these things that give him his actual standing, and it is from this vantage ground that he looks around him. — I. Taylor

When the server wins this point, it is called vantage in; when the receiver, or striker out, wins, it is called vantage out.

Vantage , transitive verb

To profit; to aid. [Obsolete] — Spenser