Discovered Everyman wearing large amount of make-up (10)
I believe the answer is:
foundation
'make-up' is the definition.
(makeup for the face to give even complexion)
'discovered everyman wearing large amount' is the wordplay.
'discovered' becomes 'found' ('find' can be a synonym of 'discover').
'everyman' becomes 'i' (where 'Everyman' is the setter of the crossword).
'wearing' is an insertion indicator.
'large amount' becomes 'a ton'.
'i' placed within 'aton' is 'ation'.
'found'+'ation'='FOUNDATION'
'of' is the link.
(Other definitions for foundation that I've seen before include "Groundwork, basis" , "Underlying basis" , "Base" , "cosmetic aid?" , "Artificial jet of water" .)