Being upset about sonnet, perhaps will eat away at them (5)
I believe the answer is:
erode
'will eat away at them' is the definition.
I can't tell whether this definition defines the answer.
'being upset about sonnet' is the wordplay.
'being upset' says the letters should be written in reverse.
'about' becomes 're' (regarding).
'sonnet' becomes 'ode' (I've seen this in another clue).
're' written backwards gives 'er'.
'er'+'ode'='ERODE'
'perhaps' is the link.
Can you help me to learn more?
(Other definitions for erode that I've seen before include "Become ground down or deteriorate" , "'Deteriorate, wear away (5)'" , "Gradually wear away" , "Eat away" , "Corrode" .)