Chaste lady on vacation avoiding excess (8)
I believe the answer is:
modestly
'avoiding excess' is the definition.
(modest can mean avoiding excess)
'chaste lady on vacation' is the wordplay.
'chaste' becomes 'modest' (modest can mean chaste or virginal).
'on vacation' means to remove the middle letters (after the inside letters have vacated the word).
'lady' with its middle removed is 'ly'.
'modest'+'ly'='MODESTLY'
(Other definitions for modestly that I've seen before include "In unassuming manner" , "without boasting" , "Unassumingly" , "in low-key fashion" , "Fairly" .)