Gross salary originally received by old worker (5)
I believe the answer is:
obese
'gross' is the definition.
(thesaurus)
'salary originally received by old worker' is the wordplay.
'originally' says to take the initial letters.
'received by' indicates putting letters inside.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'worker' becomes 'bee' (a worker bee).
The initial letter of 'salary' is 's'.
'o'+'bee'='obee'
's' going inside 'obee' is 'OBESE'.
(Other definitions for obese that I've seen before include "Dangerously corpulent" , "Needing to lose weight" , "getting well-upholstered" , "Extremely overweight" , "Grossly fat" .)