Van went fast to catch a flightless bird (9)
I believe the answer is:
spearhead
'van' is the definition.
(thesaurus)
'went fast to catch a flightless bird' is the wordplay.
'went fast' becomes 'sped' (I've seen this before).
'to catch' means one lot of letters goes inside another.
'flightless bird' becomes 'rhea' (rhea is a kind of flightless bird).
'a'+'rhea'='arhea'
'sped' placed around 'arhea' is 'SPEARHEAD'.
(Other definitions for spearhead that I've seen before include "front" , "initiate attack" , "those at the forefront" , "Vanguard" , "Lead (a military attack)" .)