Intellectual guys converse endlessly (6)
I believe the answer is:
mental
'intellectual' is the definition.
('mental' is associated in meaning with 'intellectual')
'guys converse endlessly' is the wordplay.
'guys' becomes 'men'.
'converse' becomes 'talk' (I've seen this before).
'endlessly' means to remove the last letter.
'talk' with its final letter removed is 'tal'.
'men'+'tal'='MENTAL'
(Other definitions for mental that I've seen before include "Light allowing vehicles to turn while ahead is red" , "Nuts" , "Done in the mind" , "Lament (anag) - of the mind" , "Cerebral" .)