from
The Collaborative International Dictionary of English v.0.48
Valentine \Val"en*tine\, n.
1. A sweetheart chosen on St. Valentine's Day.
[1913 Webster]
2. A letter containing professions of love, or a missive of a
sentimental, comic, or burlesque character, sent on St.
Valentine's Day.
[1913 Webster]
{St. Valentine's Day}, a day sacred to St. Valentine; the
14th of February. It was a very old notion, alluded to by
Shakespeare, that on this day birds begin to mate. Hence,
perhaps, arose the custom of sending love tokens at that
time.
[1913 Webster]