Hitch (a lift) (5)
I believe the answer is:
thumb
'hitch a lift' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for thumb that I've seen before include "Hitch-hiking digit" , "Digit (used for making a hitch?)" , "One opposed to other manual workers" , "Big digit" , "First digit" .)