early 14c., "to comb (flax or hemp) with a heckle;" from heckle, n. or from related Middle Dutch hekelen. Figurative meaning "to question severely in a bid to uncover weakness" is from late 18c. "Long applied in Scotland to the public questioning of parliamentary candidates" [OED]. Related: Heckled; heckling.

"flax comb," c.1300, hechel, perhaps from an unrecorded Old English *hecel or a cognate Germanic word (such as Middle High German hechel, Middle Dutch hekel), from Proto-Germanic *hakila-, from PIE *keg- "hook, tooth" (see hook, n.).