Give a name to (5)
'give a name to' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for christen that I've seen before include "Name in church" , "Baptise and name" , "Baptize" , "Use for the first time" , "attach handle to" .)
(Other definitions for label that I've seen before include "Give name to" , "Identification tag" , "Put a name to" , "Designate" , "Tag or designation" .)