1. in sexual contexts.
(a) [17C] a promiscuous man, a whoremonger.
(b) [late 17C+] the (head of the) penis.
2. in pl., as a part of the body.
(a) [late 19C+] the testicles [they ‘knock together’ but note knackers n.].
(b) [1930s+] (orig. US) the female breasts; occas. in sing.
3. a physically or socially superior individual.
(a) [17C–19C] an outstandingly attractive person or thing.
(b) [late 19C+] (US, also k’nocka) the top person, the person in authority, often in comb., e.g. head knocker under head n., top knocker [their ‘striking’ appearance].
(c) [1900s] (Aus.) the ideal, the best way.
4. a form of hair dressing seen as resembling a door-knocker.
(a) ‘a Man’s hair tied behind in a Club’ (Grose, c.1786).
(b) [early–mid-19C] a form of pendant to a wig, similar to a pigtail.
(c) [19C] a small curl worn flat on the temples, a fashionable hairstyle at that time [abbr. door-knocker n. (2)].
5. in context of communication.
(a) [late 19C+] (US Und.) an informer or complainant.
(b) [late 19C+] (orig. US) a critic, esp. one who relishes making negative comments.
(c) [1900s–50s] a criticism; negative comments; also as the knockers.
6. [1920s–30s] (UK tramp) an arrest.
7. [1920s+] in UK Und. uses.
(a) a gambler or prisoner who refuses to pay their debts (which cannot be enforced legally in the UK).
(b) one who passes bad cheques or gains goods on credit — and fails to pay the bill.
(c) (UK Und.) a scrounger.
8. see hard-hitter n.
9. see knocko n.
SE in slang uses
see knock-down n. (1b)
[late 19C–1920s] an ugly face, or the person who ‘owns’ it.
low-value goods that are sold door-to-door, mainly as a pretext for gaining an introduction to the owner, who may thus be defrauded of heirlooms and/or valuables.
[20C+] a door-to-door pedlar.
[19C] dressed in one’s best clothes.
[2000s] (N.Z.) completely drunk.
[mid-19C–1900s] to live up to one’s means.
1. [mid-19C+] (UK Und., also on the knock) touring houses, ostensibly to buy or sell goods, but spec. to trick or bully people into selling heirlooms, antiques etc. for minimal prices; thus the knocker (game), working as a fraudulent door-to-door salesman.
2. [1930s+] (Aus., also on the knob, on the knuckle) at once, on demand, esp. of cash payments, exactly.
3. [1940s] working as a door-to-door salesman.
[1910s] (Aus.) to drink to excess.
1. [mid-19C–1910s] capable, up to a task.
2. [mid-19C+] fashionably dressed or over–dressed.
3. [late 19C] in prime condition; enjoying oneself.
4. [late 19C] completely.