Several parts combine into one character.

弱 is a compound ideograph showing two bows (弓 弓) with feather-like wisps (resembling 彡, the streaks radical) drooping over each top. The picture is of two slack, drooping bows — bows that have lost their tension and gone limp. A drooping bow cannot fire an arrow; it has no strength. From this image grew the abstract sense "weak, frail, lacking force." This makes a perfect etymological pair with 強 (strong), whose original form depicted a bow tightly wrapped with insect ties for reinforcement. Tense bow strong; slack bow weak.

Korean reading "yak." 強弱 (gangyak, strong and weak — used in music for dynamics, in physics for intensity), 弱者 (yakja, the weak / underdog — a politically and socially loaded term), 虛弱 (heoyak, frail / sickly), 脆弱 (chwiyak, vulnerable / fragile), 弱點 (yakjeom, weak point / Achilles' heel), 老弱 (noyak, "old and weak" = the elderly and infirm). The character spans physical, social, and metaphorical weakness with equal ease.

Mandarin ruò, 4th tone. 弱 (ruò, weak), 弱点 (ruòdiǎn, weak point), 虚弱 (xūruò, frail), 弱小 (ruòxiǎo, weak and small / disadvantaged), 软弱 (ruǎnruò, soft and weak / spineless). Modern Chinese internet slang adopted 弱 as a verbal jab in gaming and online discussion: "你太弱了" (nǐ tài ruò le, "you're so weak") is a standard insult between gamers — like English "you suck."

Japanese on-reading ジャク (jaku) — 弱点 (jakuten, weak point), 虚弱 (kyojaku, feeble), 弱者 (jakusha, the weak), 弱小 (jakushō, weak and small). Two kun-readings: よわい (yowai, "weak") for the adjective state, and よわる (yowaru, "to grow weak") for the verb of becoming weak. Japanese has a particularly strong tradition of using 弱 for emotional / psychological weakness: 気が弱い (ki ga yowai, "weak-spirited") describes a timid or fainthearted person, 押しに弱い (oshi ni yowai, "weak to pressure") describes someone easily swayed. The mental and physical senses share the same kun-reading without distinction.

Memory aid: two drooping bows with feather-like wisps falling from their tops — bows gone slack are weak. Pair with 強 (taut bow = strong).