First mate biting lip (6)
I believe the answer is:
primal
'first' is the definition.
(primal can mean early or first)
'mate biting lip' is the wordplay.
'mate' becomes 'pal' (I've seen this in another clue).
'biting' means one lot of letters goes inside another (some letters bite or swallow others).
'lip' becomes 'rim' (synonyms).
'pal' enclosing 'rim' is 'PRIMAL'.
(Other definitions for primal that I've seen before include "First; primitive" , "Primeval, original" , "Original, fundamental" , "Primitive or fundamental" , "Relating to an early stage of evolution" .)