The Collaborative International Dictionary of English v.0.48:
Retard \Re*tard"\, v. t. [imp. & p. p. Retarded; p. pr. & vb.
n. Retarding.] [L. retardare, retardatum; pref. re- re- +
tardare to make slow, to delay, fr. tardus slow: cf. F.
retarder. See Tardy.]
1. To keep delaying; to continue to hinder; to prevent from
progress; to render more slow in progress; to impede; to
hinder; as, to retard the march of an army; to retard the
motion of a ship; -- opposed to accelerate.
2. To put off; to postpone; as, to retard the attacks of old
age; to retard a rupture between nations.
Syn: To impede; hinder; obstruct; detain; delay;
procrastinate; postpone; defer.