Part of the body whose technical name is the pollex (5)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
thumb
(Other definitions for thumb that I've seen before include "Hitch-hiker's tool" , "One opposed to other manual workers" , "''Tom ..., the piper's son'' (nursery rhyme)" , "Pollex, in humans" , "Tom's digit" .)