Commit to memory name of king, northern (5)
I believe the answer is:
learn
'commit to memory' is the definition.
(synonyms)
'name of king northern' is the wordplay.
'name of king' becomes 'lear' (Shakespeare's King Lear).
'northern' becomes 'n' (abbreviation e.g. N. Ireland).
'lear'+'n'='LEARN'
(Other definitions for learn that I've seen before include "Be educated" , "Ascertain" , "Become aware of" , "Pick up" , "Hear - memorise" .)