dot belowḅ

A single dot under the vowel, the Vietnamese nặng tone. mạ, mẹ, học, một, bạn, lạnh. Outside Vietnamese the same mark appears in Yoruba, Igbo and in IAST transliteration of Sanskrit, where it marks retroflex consonants such as ṭ, ḍ, ṇ and ṣ.

Combining mark: U+0323