Unbalanced people talk without end (6)
I believe the answer is:
mental
'unbalanced' is the definition.
(thesaurus)
'people talk without end' is the wordplay.
'people' becomes 'men' (man is a kind of person).
'without end' means to remove the last letter.
'talk' with its final letter taken away is 'tal'.
'men'+'tal'='MENTAL'
(Other definitions for mental that I've seen before include "Involving the mind" , "Lament (anag) - of the mind" , "like brain operation" , "Relating to the mind" , "Pertaining to the mind" .)