固まる

かたまる · katamaru · JLPT N2 · verb-godan

to harden

🧊 固 (katai: hard, solid) + まる (become) = become hard, harden, solidify

The kanji 固 means hard or solid, as in 固い (katai). まる marks a change of state, so 固まる means turning solid, like water setting into ice.