noun
safe tile (mahjong)
In mahjong, a tile that can be discarded with little risk of giving an opponent an advantage.
安全牌を切って、とりあえず凌いだ。
I discarded a safe tile and managed to get by for the moment.
noun
safe choice; no-risk option
Idiomatic extension from mahjong: a person or thing that poses no risk or is easy to deal with. Often used for a safe romantic partner or a low-risk decision.
彼は安全牌だから、紹介しても安心だ。
He's a safe choice, so I feel comfortable introducing him.
このプランは安全牌で、失敗する心配はない。
This plan is a no-risk option; there's no worry about it failing.