Binge before cutting old tax (7)
I believe the answer is:
overeat
'binge' is the definition.
(synonyms)
'before cutting old tax' is the wordplay.
'before' becomes 'ere' (poetic term for 'before').
'cutting' means one lot of letters goes inside another (some letters cut their way into a word).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'tax' becomes 'VAT' (British sales tax).
'o'+'vat'='ovat'
'ere' going within 'ovat' is 'OVEREAT'.
(Other definitions for overeat that I've seen before include "Consume excessively" , "pig out?" , "Binge" , "Be gluttonous" , "Be greedy" .)