ob·li·gate /'ä-blə-ˌgāt/ vt -gat·ed, -gat·ing
1: to bind legally or morally
was obligated to pay child support
2: to commit (as funds or property) to meet or provide security for an obligation
oblig·a·to·ry /ə-'bli-gə-ˌtōr-ē/ adj
Merriam-Webster’s Dictionary of Law. Merriam-Webster. 1996.