緩める
ゆるめる · yurumeru · JLPT N1 · verb-ichidan
to loosen
🐢 緩 = thread-like silk loosened; 緩める: loosen the 糸 knot, so slow down
Kanji 緩 combines 糸 (thread) and 爰 (a pull that gives way). Loosening a thread slows its tension, so the same verb covers both 'loosen' and 'slow down'.