极端
jíduān · HSK 6
extreme
⚡ 极 utmost + 端 end = the utmost end, the extreme
极 means pole or utmost, 端 means end or tip. Together they point to the farthest possible end of any scale — the extreme.
极 — wood radical 木 + 及 (jí, phonetic)
极 is a semantic-phonetic compound: 木 (wood) hints at the meaning, since the original sense was the ridgepole — the highest beam of a roof. 及 supplies the sound 'jí'. From 'topmost beam' the meaning extended to 'extreme, utmost, pole', as in 北极 (North Pole).
端 — 立 stand + 耑 (phonetic, sprout)
端 combines 立 'to stand' with phonetic 耑, which originally depicted a plant sprouting with roots and shoots — its tips at both ends. The semantic 立 reinforces 'upright,' giving 端 meanings like 'end, tip, extremity' and by extension 'upright, proper.'