Several parts combine into one character.

Phonetic-semantic compound: 女 (woman) + 台 (a phonetic with the historical sense of "platform / foundation"). The original meaning anchors "beginning" in human procreation — a woman conceiving / receiving life. The most foundational "first / start" is the start of a life. Identical across 繁體 / 新字体 / 简体. Pairs perfectly with 終 / 终 (end) — 始終 (shǐzhōng / shijū / 시종) means "from beginning to end" in all three languages.

Mandarin: shǐ, dipping 3rd tone. 开始 (kāishǐ, to begin / the beginning) is the everyday word — every Chinese textbook chapter starts with the word 开始. 始终 (shǐzhōng, "from start to finish" / "always"), 原始 (yuánshǐ, original / primitive), 创始 (chuàngshǐ, to found / inaugurate), 始祖 (shǐzǔ, founder / progenitor).

Japanese: on-reading シ (shi) for compounds — 開始 (kaishi, start), 始発 (shihatsu, first train / first departure — every Japanese commuter knows this word), 原始 (genshi, primitive / primeval — 原始時代 = prehistoric era), 創始者 (sōshisha, founder). Kun-reading は.じめる (haji.meru, to start something — transitive) and は.じまる (haji.maru, to begin — intransitive). The transitive/intransitive pair はじめる/はじまる is one of the foundational verb-pairs: 私は仕事を始める (I start work) vs 仕事が始まる (work starts).

始発 (shihatsu) — "first departure" — is essential vocabulary for anyone using Japanese trains. The first 始発電車 (shihatsu densha) of the morning is around 5:00 AM in Tokyo and is a cultural touchstone — there are 始発で帰る (going home on the first train, after staying out all night) and 始発で行く (catching the first train) phrases that anchor entire Japanese social rituals.

Memory aid: woman + foundation — life beginning, the most fundamental "start".