Lewis & Short

ad-dĕcet, ēre, 2, v. impers. [ad, intens.], it behooves, it becomes, it is fit or proper that (used only in Enn. and Plaut., in the latter very often), constr. with acc. or with acc. and inf.: sed virum virtute vera vivere animatum addecet, Enn. ap. Gell. 7, 17, 10 (Trag. v. 338, ed. Vahl.; Rib. p. 52): ut matrem addecet familias, Plaut. Merc. 2, 3, 80: meo me aequum est morigerum patri, ejus studio servire addecet, id. Am. 3, 4, 21; nam peculi probam nihil habere addecet Clam virum, id. Cas. 2, 2, 26; so id. Bacch. 1, 2, 20; id. Most. 4, 2, 21; id. Ps. 1, 5, 156; id. Trin. 1, 2, 41.