Several parts combine into one character.

辛 has a startling origin: the original pictograph depicted a sharp tattooing or branding implement used in ancient China to mark criminals on the forehead. The character thus encodes "what causes piercing pain" — and from this gruesome tool grew two related abstract meanings that survive in modern usage: physical "spicy / pungent" (the piercing sensation on the tongue) and emotional "painful / hardship" (the piercing experience of suffering). One character spans tongue and soul. Whenever 辛 appears as a component in other characters (辭, 辨, 親 etc.), it usually carries the connotation of pain or sharpness.

Korean reading "sin." 辛苦 (singo, hardship — formal, used in "to undergo hardship"), 辛味 (sinmi, spicy taste), 辛香 (sinhyang, spicy fragrance), 五辛菜 (osinchae, "five spicy vegetables" — a classical Korean Buddhist food taboo, the five pungent vegetables monks abstain from), 歲辛 (sesin, year of toil). And most globally famous: 辛라면 (Sin Ramyun) — the Korean Nongshim ramyun brand whose name uses this exact character to mark its signature spicy flavor; the red package with 辛 is recognizable in supermarkets worldwide.

Mandarin xīn, 1st tone. 辛 (xīn), 辛苦 (xīnkǔ, "spicy-bitter" = hardship / hard work), 辛酸 (xīnsuān, "spicy-sour" = bitter and painful / life's sorrows), 辛辣 (xīnlà, "spicy-hot" = pungent both literally and figuratively, used for sharp criticism). The phrase 辛苦了 (xīnkǔle, "you've worked hard") is one of the most ubiquitous courteous expressions in Chinese — said to anyone who has just completed effort. 新加坡 (Xīnjiāpō, Singapore) uses 新 (new) for the "Sin-" sound, not 辛.

Japanese on-reading シン (shin) — 辛苦 (shinku, hardship), 香辛料 (kōshinryō, "fragrant-spicy material" = spices). Two famously distinct kun-readings split the meaning: からい (karai, "spicy / pungent" — taste sensation: 辛いカレー karai karē "spicy curry"); つらい (tsurai, "painful / tough / heart-wrenching" — emotional state: 辛い経験 tsurai keiken "painful experience"). Same kanji 辛い, two readings, two completely different domains. This split is one of the most-tested kun-reading distinctions on Japanese language exams.

Memory aid: a sharp tattooing tool — what pierces the skin pierces the tongue (spicy) and the heart (suffering).