"Hieroglyphic" is a word in ENGLISH

Alt. of Hieroglyphical

A sacred character; a character in picture writing,
as of the ancient Egyptians, Mexicans, etc. Specifically, in the
plural, the picture writing of the ancient Egyptian priests. It is made
up of three, or, as some say, four classes of characters: first, the
hieroglyphic proper, or figurative, in which the representation of the
object conveys the idea of the object itself; second, the ideographic,
consisting of symbols representing ideas, not sounds, as an ostrich
feather is a symbol of truth; third, the phonetic, consisting of
symbols employed as syllables of a word, or as letters of the alphabet,
having a certain sound, as a hawk represented the vowel a.

Any character or figure which has, or is supposed to
have, a hidden or mysterious significance; hence, any unintelligible or
illegible character or mark.