dấu ngã

Etymology
(from the fact that the word ngã has the tone written with a tilde).

The diacritic itself derives from the Greek, which is a.

Noun

 * 1)  tilde tone mark in Vietnamese
 * 2)  creaky rising tone

Usage note
This diacritic is a homoglyph of or, which refer to diacritical marks that resemble the tilde but do not carry the same meaning. The Portuguese was adopted by the original Vietnamese alphabet as, which has fallen out of use.