Thus a learner can be 'King' (3)
I believe the answer is:
sol
'be king' is the definition.
The answer and definition can be both people as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'thus a learner' is the wordplay.
'thus' becomes 'so' (synonyms).
'a learner' becomes 'l' (as in a learner driver with L-plates on their car).
'so'+'l'='SOL'
'can' acts as a link.
Can you help me to learn more?
(Other definitions for sol that I've seen before include "Roman sun-god" , "The sun in Spain" , "Mexican lager" , "Roman counterpart of Helios" , "The sun in 12 Across" .)