Chin rest's alternative name (8)
I believe the answer is:
christen
'name' is the definition.
(I know this)
'chin rest's alternative' is the wordplay.
'alternative' indicates an anagram.
'chin'+'rest'='chinrest'
'chinrest' anagrammed gives 'CHRISTEN'.
(Other definitions for christen that I've seen before include "attach handle to" , "Give a name to (baby)" , "Baptize" , "Baptise and name" , "Use for the first time" .)