Name Spike (after farewell) as sweetheart (9)
I believe the answer is:
valentine
'sweetheart' is the definition.
(I know that valentine is a type of sweetheart)
'name spike after farewell' is the wordplay.
'name' becomes 'n' (common abbreviation e.g. on forms).
'spike' becomes 'tine' (spike of a fork).
'after' says to put letters next to each other.
'farewell' becomes 'vale' ('farewell' in Latin).
'n'+'tine'='ntine'
'ntine' after 'vale' is 'VALENTINE'.
'as' is the link.
(Other definitions for valentine that I've seen before include "Card to sweetheart" , "February lover" , "Feb 14 card" , "Saint of sweethearts" , "February patron saint of lovers" .)