A no-good royal? Similar (4)
I believe the answer is:
akin
'similar' is the definition.
('akin' can be similar in meaning to 'similar')
'a no-good royal?' is the wordplay.
'no' is a deletion indicator.
'good' becomes 'g' (abbreviation).
'royal?' becomes 'king' (I've seen this before).
'king' with 'g' taken away is 'kin'.
'a'+'kin'='AKIN'
(Other definitions for akin that I've seen before include "Having similar characteristics" , "Seemingly related" , "Related or similiar" , "Of similar character" , "Of like nature or related" .)