Parents are aggravating? The crust! (6)
I believe the answer is:
pastry
'the crust' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.
'parents are aggravating?' is the wordplay.
'parents' becomes 'pas' (pa is a kind of parent).
'are aggravating?' becomes 'try' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'pas'+'try'='PASTRY'
Can you help me to learn more?
(Other definitions for pastry that I've seen before include "Choux --; puff --" , "See 7 Down" , "Pie base" , "Dough made from flour, fat and water" , "Dough made for pies, etc." .)