Competent learner in Lincoln (4)
I believe the answer is:
able
'competent' is the definition.
(similar in meaning)
'learner in lincoln' is the wordplay.
'learner' becomes 'l' (as in a learner driver with L-plates on their car).
'in' indicates putting letters inside.
'lincoln' becomes 'abe' (Abraham Lincoln).
'l' going into 'abe' is 'ABLE'.
(Other definitions for able that I've seen before include "Competent as, say, sailor" , "Skilled" , "Competent - sort of seaman" , "With the required capacities" , "Fitted" .)