Aged heads of organisation leave dutifully (3)
I believe the answer is:
old
'aged' is the definition.
(similar in meaning)
'heads of organisation leave dutifully' is the wordplay.
'heads of' suggests taking the first letters.
The initial letters of 'organisation leave dutifully' is 'OLD'.
(Other definitions for old that I've seen before include "No longer young" , "At an early stage - at a late stage" , "Elderly" , "Ancient" , "Wild clematis" .)