My grandfather's diary was written in almost illegible hieroglyphics.

hieroglyphics 是名词，来自希腊语，由 hiero-（神圣的）和 glyph（雕刻）组成，原指古埃及的象形文字。在现代英语中引申为"难以辨认的字迹"或"天书般的符号"。