The kanji shows a person bending forward, pointing to the ground, to the low, the foundational, the root of a family. That connects 氏 to 底 (soko, bottom) and 低 (hikui, low): the foundation your family is built on. So 彼氏 (kareshi)? It combines 彼 (kare, "that/he") with 氏 (shi) as a formal way to refer to a person: "that gentleman. " In old Japan, knowing someone's 氏 (uji) told you everything: their rank, their ancestors, their place in society. Now 彼氏 (kareshi) just means your boyfriend.