Frank may be the son (6)
I believe the answer is:
honest
'frank' is the definition.
(similar in meaning)
'may be the son' is the wordplay.
'may be' indicates an anagram.
'the'+'son'='theson'
'theson' anagrammed gives 'HONEST'.
(Other definitions for honest that I've seen before include "Trustworthy or candid" , "Sincere, truthful" , "Fair and free of deceit" , "Sincere, upright" , "Not cheating, just" .)