Where the shape comes from
Hair hanging from a chin: the top line is the face, and the strokes below are the strands of a beard. The graph was borrowed early for the grammatical word ér "and, yet", and the beard sense was left to 耐 and to compounds. As a component it survives in 需 and 耐; on its own it is the everyday connective of written Chinese.
汉字 filed under 而
No published character on HSK Guide is filed under this radical yet. 汉字库.