The hiragana syllable ふ(fu). Its equivalent in katakana is フ(fu). It is the twenty-eighth syllable in the gojūon order; its position is は行う段(ha-gyō u-dan, “row ha, section u”).
From Old Japanese-pu. Possibly a contraction of the 連用形(ren'yōkei, “continuative or compounding form”) of verbs and the verb 合ふ(afu, “to meet; [as an auxiliary] to do something together”).[1] Alternatively from the 未然形(mizenkei, “incomplete form”) of verbs and the verb 経(fu, “to pass, to go by [such as time]”).[1]
Via regular sound changes and later orthographic reforms, this suffix has become う(-u) in modern Japanese. This often underwent a shift to the 下二段(shimo nidan, “lower bigrade”) conjugation pattern, later 下一段(shimo ichidan, “lower monograde”), appearing as ふる(-puru) in Old Japanese, ふる(-furu) or へる(-feru) in classical Japanese, and as える(-eru) in modern Japanese.
No longer productive. Verbs that contain this suffix have generally been lexicalized and are treated as their own independent words, rather than as conjugations or aspects of the root verbs.