A nettle blown about caught arm (8)
I believe the answer is:
tentacle
'arm' is the definition.
(I've seen this before)
'a nettle blown about caught' is the wordplay.
'blown' is an anagram indicator (to blow can mean to disrupt or scatter).
'about' means one lot of letters goes inside another.
'caught' becomes 'ac' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'nettle' is an anagram of 'tentle'.
'tentle' going around 'ac' is 'TENTACLE'.
(Other definitions for tentacle that I've seen before include "Arm of an octopus" , "Slender flexible limb" , "Long appendage" , "Long, boneless limb in some animals" , "Octopus's "arm"" .)