From WordNet (r) 3.0 (2006) [wn]:
birthday
n 1: an anniversary of the day on which a person was born (or
the celebration of it)
2: the date on which a person was born [syn: birthday, {natal
day}]
From The Collaborative International Dictionary of English v.0.48 [gcide]:
Birthday \Birth"day`\, a.
Of or pertaining to the day of birth, or its anniversary; as,
birthday gifts or festivities.
[1913 Webster]
From The Collaborative International Dictionary of English v.0.48 [gcide]:
Birthday \Birth"day`\ (b[~e]rth"d[=a]`), n.
1. The day in which any person is born; day of origin or
commencement.
[1913 Webster]
Those barbarous ages past, succeeded next
The birthday of invention. --Cowper.
[1913 Webster]
2. The day of the month in which a person was born, in
whatever succeeding year it may recur; the anniversary of
one's birth.
[1913 Webster]
This is my birthday; as this very day
Was Cassius born. --Shak.
[1913 Webster]