Pierced one's skin (5)
I believe the answer is:
cutis
'skin' is the definition.
(I've seen this before)
'pierced one's' is the wordplay.
'pierced' becomes 'cut' ('cut' can be similar in meaning to 'pierced').
'one's' becomes 'is' (roman numeral).
'cut'+'is'='CUTIS'
(Other definitions for cutis that I've seen before include "a bit skinny" , "Technical name for skin" , "Skin, dermis" , "Surface area" , "skin, technically" .)