to gamble at the common table game in casino called 'over-under or O/U'; to take a gamble at something risky and unpredicatable [colloquial]
Definitions (粵典–words.hk)
動詞、名詞
一種賭博。用骰賭大細(又稱買骰寶)，用三粒骰仔響密封的骰盅入面搖動，使之得出任意嘅總數。總數4-10點為開細，11-17點為開大，三粒骰點數一樣叫圍骰，大小通殺。 sic bo; tai-sai; big and small; hi-lo; a gambling game; players bet on "big", "small" or "triples", then 3 dice are rolled to get a total score, 4-10 is "small", 11-17 is "big", and 3 dice showing the same number is called "triples"
呢單生意好似買大細咁，好大風險好難估喎。
呢单生意好似买大细咁，好大风险好难估㖞。
lei1 daan1 saang1 ji3 hou2 ci5 maai5 daai6 sai3 gam2, hou2 daai6 fung1 him2 hou2 naan4 gu2 wo3 This deal just like betting on Tai-Sai, so risky and unpredictable.
買大開細，買細開大，今日真係唔好彩。
买大开细，买细开大，今日真系唔好彩。
maai5 daai6 hoi1 sai3, maai5 sai3 hoi1 daai6, gam1 jat6 zan1 hai6 m4 hou2 coi2 Bet small and got a big, bet big and got a small, so unlucky today.