ẖ

H with macron below (unicode|H̱ ẖ) transliterates:
*Arabic unicode|ẖāʼ (ﺥ) (also as ḫ)
*Hebrew unicode|ẖet (ח) (also as ḫ)
*Egyptian hieroglyph X

Unicode

Unicode unicode|ẖ U+|1E96 "Latin small letter h with line below" is canonically equivalent to unicode|ẖ (U+0068 U+0331).

Note that Unicode does not reserve a codepoint for a "Latin capital letter H with line below". Therefore, a sequence with a combining diacritic "macron below" must be employed: unicode|H̱ (U+0048 U+0331). This lack of a precomposed character may pose a problem for some layout engines.