'To knock on the head' definitions:

Definition of 'To knock on the head'

From: GCIDE

Knock \Knock\ (n[o^]k), v. t.
1. To strike with something hard or heavy; to move by striking; to drive (a thing) against something; as, to knock a ball with a bat; to knock the head against a post; to knock a lamp off the table. [1913 Webster]
When heroes knock their knotty heads together. --Rowe. [1913 Webster]
2. To strike for admittance; to rap upon, as a door. [1913 Webster]
Master, knock the door hard. --Shak. [1913 Webster]
3. To impress strongly or forcibly; to astonish; to move to admiration or applause. [Slang, Eng.] [Webster 1913 Suppl.]
4. To criticise; to find fault with; to disparage. "Don't knock it if you haven't tried it." [PJC]
To knock in the head, or To knock on the head, to stun or kill by a blow upon the head; hence, to put am end to; to defeat, as a scheme or project; to frustrate; to quash. [Colloq.] -- To knock off. (a) To force off by a blow or by beating. (b) To assign to a bidder at an auction, by a blow on the counter. (c) To leave off (work, etc.). [Colloq.] -- {To knock out}, to force out by a blow or by blows; as, to knock out the brains.
To knock up. (a) To arouse by knocking. (b) To beat or tire out; to fatigue till unable to do more; as, the men were entirely knocked up. [Colloq.] "The day being exceedingly hot, the want of food had knocked up my followers." --Petherick. (c) (Bookbinding) To make even at the edges, or to shape into book form, as printed sheets. (d) To make pregnant. Often used in passive, "she got knocked up". [vulgar]