Lat He undertook; he promised. A promise or engagement by which one person assumes or undertakes to do some act or pay something to another. It may be either oral or in writing, but is not under seal. It is express if the promisor puts hls engagement in distinct and definite language; it is implied where the law infers a promise (though no formal one has pussed) from the conduct of the party or the clr-cumstances of the case