à cheval

à cheval

(a ʃəval)
adv
(Gambling, except Cards) (of a bet, esp in roulette) made on two adjacent numbers, cards, etc
[literally: on horseback]
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014