obliger - v.
1 tr. (foll. by to + infin.) constrain, compel.
2 tr. be binding on.
3 tr. a make indebted by conferring a favour. b (foll. by with, or by + verbal noun) gratify (oblige me by leaving). c perform a service for (often absol.: will you oblige?).
4 tr. (in passive; foll. by to) be indebted (am obliged to you for your help).
5 intr. colloq. (foll. by with) make a contribution of a specified kind (Doris obliged with a song).
6 tr. archaic or Law (foll. by to, or to + infin.) bind by oath, promise, contract, etc.

much obliged an expression of thanks.

obliger n. [ME f. OF obliger f. L obligare (as OB-, ligare bind)]