to get a ride from a passing motorist; to make a sign with one's thumb that indicates to passing drivers that one is asking for a ride. My car broke down on the highway, and I had to thumb a ride to get back to town. Sometimes it's dangerous to hitch a ride with a stranger.
tv. to beg a ride; to stand at the side of the street and signal to cars with one’s thumb for a ride; to hitchhike. I’ll thumb a ride to get there if I have to.