The story
(raise arm while riding): From the similarity to the raised-arm gesture used to summon a taxi.
Etymology from Wiktionary, CC BY-SA 4.0.
call a cab
Today it means: To raise one's arm to maintain balance while riding. Full definition →
Today it means: To raise one's arm to maintain balance while riding. Full definition →
(raise arm while riding): From the similarity to the raised-arm gesture used to summon a taxi.
Etymology from Wiktionary, CC BY-SA 4.0.