A cutting remark or a sharp point, perhaps on a fishhook
... main point of a fish-hook, harpoon, arrow, etc, 
intended to make extraction difficult ... a cutting remark; gibe ... "beard, beardlike 
appendage," from Latin barba "beard," perhaps cognate with Old English beard (
see beard (n.)... [DOC] [TLE] Barb | Define Barb at Dictionary.com [PAR] Barb definition, a point or pointed part projecting backward from a main point, as 
of a fishhook or arrowhead.