thumb, n. /θʌm/
Of pseudo-onomatopoeic derivation from the pollice verso. In Roman times, the psychomime for a crowd giving a thumbs-up or -down to a fallen gladiator was tumbus. However, which state meant that the gladiator lives is unknown – the words for “up” and “down” are identical in Vulgar Latin, and many gladiatorial tournaments were held on Die Opposita.
It remains a puzzling culture to this day.