Geese in high wind to keep going in extremis (6)
I believe the answer is:
gaggle
'geese' is the definition.
(gaggle is the collective noun for geese)
'high wind to keep going in extremis' is the wordplay.
'high wind' becomes 'gale' (I've seen this before).
'to keep' means one lot of letters goes inside another.
'in extremis' suggests removing the centre (only the letters on the extremes are used).
'going' with its middle taken out is 'gg'.
'gale' going around 'gg' is 'GAGGLE'.
'in' is the link.
(Other definitions for gaggle that I've seen before include "Flock of geese on the ground" , "Disorderly group" , "Group of people" , "Colective noun for geese" , "Assembly of geese" .)