Product, primarily, in nut tree fluid (10)
I believe the answer is:
turpentine
'product primarily in nut tree fluid' is the definition.
I can't judge whether this defines the answer.
'product primarily in nut tree fluid' is the wordplay.
'primarily' indicates taking the first letters.
'fluid' is an anagram indicator.
The first letter of 'product' is 'p'.
'p'+'in'+'nut'+'tree'='pinnuttree'
'pinnuttree' is an anagram of 'TURPENTINE'.
(Other definitions for turpentine that I've seen before include "Solvent" , "artist's stuff" , "Oil used in varnishes" , "Paint/varnish spirit" , "Oil used in mixing paints" .)