Gormless second mate with basic urges (6)
I believe the answer is:
stupid
'gormless' is the definition.
('stupid' can be similar in meaning to 'gormless')
'second mate with basic urges' is the wordplay.
'second' becomes 's' (common abbreviation).
'mate' becomes 'tup' (both can mean to copulate).
'with' means one lot of letters go next to another.
'basic urges' becomes 'id' (Freudian term).
's'+'tup'+'id'='STUPID'
(Other definitions for stupid that I've seen before include "Dull" , "Obtuse" , "Unintelligent, really thick" , "Not intelligent, foolish" , "Idiot" .)