Felicitate \fi-LIS-i-teyt\ , verb;
1. To compliment upon a happy event; congratulate
2. Archaic: to make happy
This word is first attested in the 1620's with the definition "to render happy". A short 10 or so years later it had already changed a little to mean "to reckon happy." If you 'render' someone happy you make them that way, but if you 'reckon' them happy you merely recognize them as such and don't take an active roll. This difference is illustrated by the usage of felicitate as a congratulatory word (also from the 1630's). It comes from Latin felicitatus, which is the past participle of felicitare ("to make happy"). Felicitare comes from felicitas ("fruitfulness, happiness") which derives from felix. Felix (genetive: felicis) means "happy, fortunate, fruitful, fertile" and comes from the Latin base *fe-, which is the equivalent of Proto-Indo-European *dhe(i)- ("to suck, suckle, produce, yield").
Today's word and the first definition were both taken from Dictionary.com's 'Word of the Day' for Saturday, January 15
Etymologies come from the Oxford English Dictionary and/or Etymonline.com