Nibble away at my caviar? Penny tucks into it (7)
I believe the answer is:
corrode
'nibble away' is the definition.
(thesaurus)
'my caviar? penny tucks into it' is the wordplay.
'my' becomes 'cor' (both are expressions of surprise).
'caviar?' becomes 'roe' (fish eggs).
'penny tucks' becomes 'd' (I can't explain this - if you can you should give a lot more credence to this answer).
'into it' is an insertion indicator.
'roe' enclosing 'd' is 'rode'.
'cor'+'rode'='CORRODE'
'at' is the link.
Can you help me to learn more?
(Other definitions for corrode that I've seen before include "Eat away, rust" , "Eg, to rust" , "Gradually eat away" , "Chemically weaken" , "Oxidise" .)