What does anyone and everyone see when looking at this glyph?…a line segment, that is, ONE segment. Nonetheless, a segment is comprised of an ARRAY of an infinite number of points directly between a designated starting point and a designated ending point. And what else can be seen? Something HORIZONTAL. Furthermore, a ROD or SHAFT is clearly evident, similar to 丨 but with a different orientation. Every time「一」is drawn, the writer experiences the meaning of LATERAL MOTION of the hand, and the brush or pen in hand.
　Be sure to review the older glyphs meaning SINGULAR: 壹, 壱, 弌 referring to that singular event in all of biology, that being beyond what is ordinary, especially in being exceptionally good and remarkable. The sequence of changing elements within the glyphs depict the evolving customs in ancient humans, particularly in China. A geometric line may be conceptualized as an infinite array of points as Euclid described, and this element can refer to an ARRAY, or to items that have been ARRAYED AS ONE LINE: a segment of a line is an array of points or dots, and simplified Chinese uses either ー (「repeated」) or 一 (「one」) as equivalents to replace an array or「line of drops」(灬).
　ONE, something LATERAL or HORIZONTAL, or in LATERAL MOTION (see 入, ⺄, or 永, as examples). Also used to indicate HOW WIDE something or another element is (note the top of 未 and 末, as examples). The numerals one through ten are all associated with hand gestures, used in China to avoid confusion while bargaining or simply due to pronunciation problems using different dialects, or while bidding at an auction and keeping the bid quiet, and ONE was a single finger pointing horizontally. In some glyphs, and with some fonts, this stroke appears identical to either the various「marker」strokes (such as 丶), or as「repeated bobbing head」(ー).

Used within names (nanori)
かず　･　い　･　いっ　･　いる　･　かつ　･　かづ　･　てん　･　はじめ　･　ひ　･　ひとつ　･　まこと