From The Collaborative International Dictionary of English v.0.48:
-ard \-ard\, -art \-art\
The termination of many English words; as, coward, reynard,
drunkard, mostly from the French, in which language this
ending is of German origin, being orig. the same word as
English hard. It usually has the sense of one who has to a
high or excessive degree the quality expressed by the root;
as, braggart, sluggard.
[1913 Webster]