Tearing forms, fifty complete (8)
I believe the answer is:
integral
'complete' is the definition.
(thesaurus)
'tearing forms fifty' is the wordplay.
'forms' is an anagram indicator.
'fifty' becomes 'L' (Roman numeral).
'tearing' with letters rearranged gives 'integra'.
'integra'+'l'='INTEGRAL'
(Other definitions for integral that I've seen before include "Full" , "Large tin (anag.)" , "Mathematical quantity" , "Built-in -- 1 across (anag)" , "Maths function; whole" .)