noun
Used in rankings, competitions, and ordered lists to indicate the top position.
彼はマラソンで一位になった。
He took first place in the marathon.
このレストランは地元で一位にランクされている。
This restaurant is ranked first in the local area.
noun
units place; ones digit
Refers to the rightmost digit in a decimal number, the position for 1–9. Common in math contexts or when explaining place value.
123の一位は3です。
The units digit of 123 is 3.
一番 is a more general word for 'first' or 'number one' and can be used as an adverb meaning 'most'. 一位 is specifically a rank or position in a formal ranking.
一の位 is a more explicit and common way to say 'units place' in math contexts. 一位 is a shorter, more formal or technical variant.
Compound of 一 (いち, 'one') and 位 (い, 'rank, position'). The reading いちい is a straightforward combination of the on'yomi of the two kanji.