Frank following race's outsiders (7)
I believe the answer is:
sincere
'frank' is the definition.
(similar in meaning)
'following race's outsiders' is the wordplay.
'following' becomes 'since' (I can't justify this - if you can you should give a lot more credence to this answer).
'outsiders' suggests removing the centre (only the letters on the outside of the word remain).
'race' with its centre taken out is 're'.
'since'+'re'='SINCERE'
Can you help me to learn more?
(Other definitions for sincere that I've seen before include "(Of person) genuine" , "natural?" , "'Genuine, not deceitful (7)'" , "Free from deceit" , "Perfect" .)