a. [ L. onerosus, fr. onus, oneris, a load, burden: cf. F. onéreux. ] Burdensome; oppressive. “Too onerous a solicitude.” I. Taylor. [ 1913 Webster ]
Onerous cause (Scots Law), a good and legal consideration; -- opposed to gratuitous. [ 1913 Webster ]
adv. In an onerous manner. [ 1913 Webster ]