Bulky sentries outside start to expect generosity (8)
I believe the answer is:
largesse
'generosity' is the definition.
(thesaurus)
'bulky sentries outside start to expect' is the wordplay.
'bulky' becomes 'large' ('large' can be similar in meaning to 'bulky').
'outside' says to hollow out the word (remove centre letters).
'start to' says to take the initial letters.
'sentries' with its centre removed is 'ss'.
The first letter of 'expect' is 'e'.
'large'+'ss'+'e'='LARGESSE'
(Other definitions for largesse that I've seen before include "Eelgrass (anag.)" , "Magnanimous bestowal of gifts" , "Generous alms" , "Liberal gift" , "Generosity in giving gifts" .)