There's a great site here. For each definition of a word you get right, you donate ten grains of rice to the hungry (it's done via advertising). The words get harder and harder as you go along.
I was disappointed that for years I thought "pusillanimous" meant "spoiling for a fight" when actually it means "cowardly".
But it is great fun to guess a word's meaning from its struture and letters. For example, horologe is a bit of no brainer - it means "time piece". Emesis means "vomiting" - I guessed that one.
In two minutes I have given 240 grains of rice.
UPDATE: I've got up to 440 grains of rice now, but I'll have to start supper. It's addictive.