高

高 (gāo) is the basic adjective for 'tall / high.' It covers physical height (a person, building, mountain), abstract level (high price, high standard, high temperature), and metaphorical 'high' in compounds (高兴 'happy / high-spirited'). One thing English speakers should know: Chinese uses the same word 高 for both 'tall' (a tall person) and 'high' (a high mountain) — there's no separate adjective. To ask someone's height, the standard question is 你多高？ ('How tall are you?'). The opposite depends on context — 矮 (ǎi) for short people, 低 (dī) for low things or levels (低温, 'low temperature'). 高 is also a very common Chinese surname (the surname Gao). In compounds, 高 builds dozens of useful words: 高兴 (happy), 高考 (college entrance exam), 高速 (high-speed), 提高 (to raise / improve).

Memory hook: The character 高 itself looks tall — a stacked tower silhouette.