To some extent a clever feeler (8)
I believe the answer is:
tentacle
'feeler' is the definition.
(I've seen this before)
'to some extent a clever' is the wordplay.
'to some' indicates a hidden word (some of the parts of the word are used).
'TENTACLE' is hidden within 'extent a clever'.
(Other definitions for tentacle that I've seen before include "Flexible grasping organ" , "Flexible appendage on some animals" , "Appendage as on octopus" , "Long flexible feeler" , "Flexible feeling organ" .)