Wrong applications of such cavities (7)
'such cavities' is the definition.
'sinuses' can be an answer for 'cavities' (sinus is a kind of cavity). I'm not certain of the 'such' bit.
'wrong applications' is the wordplay.
'wrong' becomes 'sin' (I've seen this before).
'applications' becomes 'uses' (I've seen this before).
'of' acts as a link.
Can you help me to learn more?
(Other definitions for sinuses that I've seen before include "Top spaces", "holes in the head", "Cavities in skull connecting with nostrils", "Empty spaces".)