Tristful \TRIST-fuhl\ , adjective;
1. Full of sadness; sorrowful
According to the Oxford English Dictionary this word is a combination of trist + -ful, which is obvious. Trist is an archaic word for "sad" that comes directly from French triste ("sad") which derives from Latin tristis ("sad, sorrowful, gloomy"). Provençal trist(e), Spanish triste, Portuguese triste, and Italian tristo all come from this Latin root as well and mean approximately the same thing.
*Today's word and the first definition were both taken from Dictionary.com's 'Word of the Day' for Thursday, December 2