Whole of tin used - over-generous (8)
I believe the answer is:
integral
'whole' is the definition.
('integral' can be similar in meaning to 'whole')
'tin used over-generous' is the wordplay.
'used' indicates an anagram.
'over' shows that the letters should be reversed in order.
'generous' becomes 'large' ('large' can be similar in meaning to 'generous'**).
'large' back-to-front is 'egral'.
'tin' is an anagram of 'int'.
'int'+'egral'='INTEGRAL'
'of' is the link.
(Other definitions for integral that I've seen before include "A component and indispensable part of, like triangle" , "using no fractions" , "Relating to being complete" , "contributing to unity" , "whole thing" .)