Wiktionary
n. (context typesetting English) A tone mark ( ̉) that indicates falling then rising tone in Vietnamese.
Wikipedia
In typesetting, the hook above is a diacritic mark placed on top of vowels in the Vietnamese alphabet. In shape it looks like a tiny question mark without the dot underneath. For example, a capital A with a hook is "Ả", and a lower case "u" with a hook is "ủ". The hook is usually written to the right of the circumflex in conventional Vietnamese orthography. If Vietnamese characters are unavailable, it is often replaced by a question mark after the vowel ( VIQR encoding).
This diacritic functions as a tone marker, indicating a "mid falling" tone (): which is "dipping" (˨˩˥) in Southern Vietnamese or "falling" (˧˩) in Northern Vietnamese; see Vietnamese language § Regional variation: Tones. The Southern "dipping" tone is similar to the questioning intonation in English.
Usage examples of "hook above".
Zaranda thrust a hand in her pouch and brought forth a handful of gems and rich broaches, sparkling in the light of the single lantern hung by a hook above the slab.
After a time he pushed himself off from the wall and unhooked the dogs' leashes from the spit hook above the hearth.
Bond walked over and the man took his towel and hung his key on a hook above the box.
When they hung my wrists up on a hook above me I was sorry I'd played by the rules all those nights in the cabin when I was alone.
He climbed up on the late Count's desk and tied the end of the rope to another hook above the gaslight -- the end with the tied-on extra piece.
Using the flickering candle, Forin lit a lantern which hung on a hook above the bed, then moved to the small hearth where a fire had been laid.
Meralda found the ring on a hook above the steward's Dresser, and she took it quietly, glancing nervously at Temigast with every little noise.
She sensed being released, having a wooden frame locked over her parted ankles and hearing a chain clank over some gear or hook above.