Your setter's not ostentatious or indecent (8)
I believe the answer is:
immodest
'indecent' is the definition.
(similar in meaning)
'your setter's not ostentatious' is the wordplay.
'your setter's' becomes 'I'm' ('I'm', referring to the setter of the crossword).
'not ostentatious' becomes 'modest' (I am not sure about this - if you are sure you should believe this answer much more).
'im'+'modest'='IMMODEST'
'or' is the link.
Can you help me to learn more?
(Other definitions for immodest that I've seen before include "Conceited or indecent" , "Offending against sexual mores in appearance" , "Pretentious" , "Lacking decency, shameless" , "Indecent or shameless, perhaps in dress" .)