Stale humour starts to corrupt old and basic part of the ear (7)
I believe the answer is:
corncob
'part of the ear' is the definition.
(I've seen this before)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for corncob that I've seen before include "Hard section of a ear of maize" , "Woody core of maize" , "Head of maize" , "fodder?" , "Central part of the maize ear" .)