Liken to keeping death's-head of a friend (8)
I believe the answer is:
compadre
'a friend' is the definition.
(I've seen this before)
'liken to keeping death's-head of' is the wordplay.
'liken' becomes 'compare' ('compare' can be a synonym of 'liken').
'to keeping' is an insertion indicator.
'head of' suggests taking the first letters.
The initial letter of 'deaths' is 'd'.
'compare' going around 'd' is 'COMPADRE'.
(Other definitions for compadre that I've seen before include "American friend" , "Friend, companion" , "Friend (from Spanish)" .)