Lewis & Short

dē-dĕcet, cuit, 2, v. impers. (very rarely pers., v. infra, II.), it is unseemly, unsuitable, unbecoming: decere quasi aptum esse consentaneumque tempori et personae, etc. … contraque item dedecere, Cic. Or. 22, 74.

  1. I. Prop. (class.; usually connected with a negation), construed like decet (q. v.), with nom. or inf. rei, and with acc. pers. or absol.
        1. a.
          1. (α) Neque te ministrum dedecet myrtus neque me sub arta vite bibentem, Hor. Od. 1, 38, 7: me usus precum, Ov. M. 6, 689: nihil se, id. Rem. Am. 410. In plur.: nec dominam motae dedecuere comae, Ov. Am. 1, 7, 12; 3, 15, 4.
          2. (β) Ut, si quid dedeceat, vitemus, Cic. Off. 1, 41: vox, Quint. 11, 3, 104.
        2. b.
          1. (α) Oratorem irasci minime decet, simulare non dedecet, Cic. Tusc. 4, 25; Ov. A. A. 2, 530: togam removeri, Quint. 11, 3, 124.
          2. (β) (Togae) extremam oram rejecisse non dedecet, Quint. 11, 3, 140; Hor. Od. 2, 12, 17.
        3. c. Ut iis, quae habent, modice et scienter utantur, et ut ne dedeceat, Cic. de Or. 1, 29, 132.
  2. II. By poet. license person. as a v. a., to dishonor, neglect a thing: si non dedecui tua jussa, Stat. Th. 10, 340: Atticus Claudiorum imagines dedecere videbatur, Tac. A. 2, 43.