The Collaborative International Dictionary of English v.0.48:
Congratulate \Con*grat"u*late\, v. t. [imp. & p. p.
Congratulated; p. pr. & vb. n. Congratulating.] [L.
congratulatus, p. p. of congratulari to wish joy abundantly;
con- + gratulari to wish joy, from gratus pleasing. See
To address with expressions of sympathetic pleasure on
account of some happy event affecting the person addressed;
to wish joy to.
It is the king's most sweet pleasure and affection to
congratulate the princess at her pavilion. --Shak.
To congratulate one's self, to rejoice; to feel
satisfaction; to consider one's self happy or fortunate.
Syn: To Congratulate, Felicitate.
Usage: To felicitate is simply to wish a person joy. To
congratulate has the additional signification of
uniting in the joy of him whom we congratulate. Hence
they are by no means synonymous. One who has lost the
object of his affections by her marriage to a rival,
might perhaps felicitate that rival on his success,
but could never be expected to congratulate him on
such an event.
Felicitations are little better than
compliments; congratulations are the expression
of a genuine sympathy and joy. --Trench.