Where does “tard” come from?

Tard is not attested in Middle English retarden; the word cannot be traced through available etymological evidence.

tard (English): A person with mental retardation; A person who...

Definitions

Step	Language	Word	Meaning
1	English	retard	Retardation; delay; A slowing down of the tempo;...
2	Old French	retarder	to retard; to delay; to make late
3	Latin	retardo	I hinder, delay, detain, impede or retard
4	Latin	rĕ-	back, backwards
5	Latin	prōdūcō	to lead or bring forth, forward or out
6	Latin	prō-	forward direction, forward movement
7	Proto-Italic	*pro-	pro- see the Latin entry for further meanings
8	Proto-Indo-European	pro-	toward, forward
9	Proto-Indo-European	por-	to give birth; forward, through; going, passage
10	Proto-Indo-European	per-	before, in front; first; to go through
11	Proto-Indo-European	pr̥tós	passed , crossed