(Lat. I do that you may do.) A species of contract in the civil law(being one of the innominate contracts) which occurs when I agree with a man to dohis work for him if he will do mine for me; or If two persons agree to marry together, orto do any other positive acts on both sides; or it may be to forbear on one side inconsideration of something done on the other. 2 Bl. Comm. 444.