The compound adjective 不起眼, meaning "inconspicuous" or "unremarkable," is formed through a figurative and idiomatic process where the negating prefix 不 (not) is combined with the verb-object phrase 起眼 (literally "to rise to the eye"). The core concept 起眼 originally suggested something that "catches the eye" or "attracts attention." Therefore, by adding 不, the entire construction negates this quality, directly creating the sense of "not eye-catching." Over time, this literal visual metaphor evolved into a fixed, common term used to describe anything that fails to stand out or seems ordinary and easily overlooked.