Expert fitting round edges of device (5)
I believe the answer is:
adept
'expert' is the definition.
(synonyms)
'fitting round edges of device' is the wordplay.
'fitting' becomes 'apt' (both mean appropriate).
'round' means one lot of letters goes inside another.
'edges of' says to hollow out the word (remove centre letters).
'device' with its middle removed is 'de'.
'apt' going around 'de' is 'ADEPT'.
(Other definitions for adept that I've seen before include "Thoroughly proficient" , "clever" , "who gets the lapis philosophicus secret" , "Highly proficient" , "Having the required skills" .)