[ob.li.gate] vt -gat.ed ; -gat.ing [L obligatus, pp. of obligare] (1533) 1: to bind legally or morally: constrain
2: to commit (as funds) to meet an obligation
[2]ob.li.gate adj (1887) 1: restricted to one particularly characteristic mode of life "an ~ parasite"
2: biologically essential for survival "~ mutualism" -- ob.li.gate.ly adv