Male inventor sick about Newton becoming green (13)
I believe the answer is:
environmental
'green' is the definition.
(I've seen this before)
'male inventor sick about newton' is the wordplay.
'sick' is an anagram indicator.
'about' is an insertion indicator.
'newton' becomes 'N' (symbol for the scientific unit of force).
'male'+'inventor'='maleinventor'
'maleinventor' anagrammed gives 'evironmental'.
'evironmental' placed around 'n' is 'ENVIRONMENTAL'.
'becoming' is the link.
(Other definitions for environmental that I've seen before include "Green" , "Pertaining to the surrounding world" , "To do with one's surroundings" .)