Proper elm? Yes, surprisingly (6)
I believe the answer is:
seemly
'proper' is the definition.
(similar in meaning)
'elm? yes surprisingly' is the wordplay.
'surprisingly' indicates an anagram (a surprising ordering of the letters).
'elm'+'yes'='elmyes'
'elmyes' anagrammed gives 'SEEMLY'.
(Other definitions for seemly that I've seen before include "Decorous or proper" , "Appropriate" , "Proper, in good taste" , "Decorous, in good taste" , "Conforming to good taste" .)