Witty saying’s import regularly ignored (3)
I believe the answer is:
'witty saying's' is the definition.
(as in a bon mot)
'import regularly ignored' is the wordplay.
'regularly ignored' indicates alternate letters (letters removed at regular intervals).
The alternating letters of 'import' are 'MOT'.
(Other definitions for mot that I've seen before include "Clever remark" , "Word in France, bon perhaps" , "Irish girlfriend" , "Vehicle check" , "Witty words" .)