Expedition in which a stegosaurus is found (5)
I believe the answer is:
haste
'expedition' is the definition.
(thesaurus)
'which a stegosaurus is found' is the wordplay.
'is found' says the answer is hidden in the clue.
'HASTE' is hidden within 'which a stegosaurus'.
'in' is the link.
(Other definitions for haste that I've seen before include "Excessive speed or urgency" , "velocity" , "Expedition" , "dispatch" , "Urgency of action" .)