waiting for one tile to complete a pair with an otherwise exposed hand
Mahjong term: a tenpai state where the hand has four open melds and the player waits on a single tile to complete the pair. The wait is obvious to opponents because the rest of the hand is visible. Compare 単騎待ち, which is a single-tile wait without the exposed-hand condition.
See also: 単騎待ち (たんきまち)
I was waiting with a naked single-tile wait, but that tile never came in the end.
裸単騎は相手に待ちがばれやすい。
A naked single-tile wait makes it easy for opponents to guess what you're waiting for.
Compound of 裸 (はだか, 'naked') and 単騎 (たんき, 'single rider' or 'single tile wait'), referring to the exposed state of the hand while waiting on a single tile.