Obscure playground rumour finally true (9)
I believe the answer is:
recondite
'obscure' is the definition.
(synonyms)
'playground rumour finally true' is the wordplay.
'playground' becomes 'rec' (short for recreation ground).
'rumour' becomes 'on dit' (term for rumour - literally 'it is said' in French).
'finally' suggests the final letters.
The final letter of 'true' is 'e'.
'rec'+'ondit'+'e'='RECONDITE'
(Other definitions for recondite that I've seen before include "Abstruse" , "Difficult to understand" , "Enigmatic" , "Direct one to be obscure or difficult" , "not widely known" .)