a) a hand signal, interpreted to be negative, which consists of a fist, sideways, with the thumb pointing to the ground.
b) below Satisfactory or unacceptable.
c) An indication to kill
antonym: thumbs up
My fellow motorist gave my driving the thumbs down, before speeding off with his arm and middle finger extended.
I'm sorry, but this definition is crude, immature and a failed attempt at humour. I've just have to give it a thumbs down
The roman gladiatorial type looked about the colloseum to see row after row of thumbs down, so he cast his net over the opponent and speared him through.