Arm of an octopus (8)
I believe the answer is:
tentacle
'arm of an octopus' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for tentacle that I've seen before include "flexible arm?" , "Octopus's "arm"" , "One may be feeling" , "Flexible appendage on some animals" , "Part of octopus" .)