Tenth century “West Arabic” variation of the Nepali form of Hindu-Arabic numerals (compare Devanagari script १(1, “éka”)), possibly influenced by Roman numeral Ⅰ, both ultimately from using a single stroke to represent the number one. See 1 § As a digit on විකිපීඩියාවWikipedia for more.
(phonetics, often superscript) the pitch of a tone, either high or low depending on local convention; '1' is most commonly the highest or lowest pitch (but see 0)
(phonetics, Sinosphere, often superscript) tone number 1, typically identified with dark level yinping (陰平). May simply be level ping tone (平) if the yin–yang distinction is not made.