縮まる
ちぢまる · chidimaru · JLPT N1 · verb-godan
to shrink
🧦 縮 (shrink) + まる (become): to become shrunk, like a sweater after a hot wash
縮 carries the thread radical 糸, which fits its tightening sense. まる marks an intransitive verb, so the thing shrinks on its own, with no agent acting on it.