Number turning it green (7)
I believe the answer is:
integer
'number' is the definition.
(I know that integer is a type of number with finite decimal representations)
'turning it green' is the wordplay.
'turning' indicates anagramming the letters.
'it'+'green'='itgreen'
'itgreen' is an anagram of 'INTEGER'.
(Other definitions for integer that I've seen before include "Get Erin (anag)" , "Positive or negative whole number" , "Whole unit" , "One for example" , "Result of counting" .)