Palaeolithic tip off ... dumb, senseless repetition (9)
I believe the answer is:
echolalia
'senseless repetition' is the definition.
(I've seen this before)
'palaeolithic tip off dumb' is the wordplay.
'off' is a deletion indicator (some letters taken off).
'dumb' indicates an anagram (a foolish spelling of the letters).
'palaeolithic' with 'tip' taken away is 'alaeolhic'.
'alaeolhic' is an anagram of 'ECHOLALIA'.
(Other definitions for echolalia that I've seen before include "psychiatric problem" , "senseless repetition" , "Childish repetition of speech" , "Repetition of another's words" , "Mindless repetition" .)