Working out initially sensible following PE (11)
I believe the answer is:
operational
'working' is the definition.
(thesaurus)
'out initially sensible following pe' is the wordplay.
'initially' says to take the initial letters.
'sensible' becomes 'rational' ('rational' is associated in meaning with 'sensible'**).
'following' says to put letters next to each other.
The initial letter of 'out' is 'o'.
'rational' after 'pe' is 'perational'.
'o'+'perational'='OPERATIONAL'
(Other definitions for operational that I've seen before include "In working order" , "Ready for use" , "running" , "Ready for action" , "working satisfactorily?" .)