Green’s Dictionary of Slang

numb adj.

1. [1910s+] (US, also numbs) blind drunk; occas. intoxicated by drugs.

2. [1960s+] (US, also numbass, numbfuck) stupid.

SE in slang uses

In derivatives

numby (n.) (also nummy) [abbr. numbhead ]

[1940s+] (US) a fool, a simpleton.

In compounds

numbheaded (adj.)

[mid-18C+] (US) stupid.

numbheadedness (n.)

[1960s+] (US) stupidity.

numbnut (adj.) [numbnuts ]

[1990s+] (Aus.) foolish, stupid.

numbnuts (n.) [nuts n.2 (1)]

1. [1960s+] (US) an idiot, a fool; usu. as a term of address.

2. in attrib. use of sense 1.

numbwit (adj.) [var. on dimwit ]

[1950s+] foolish, stupid.