強まる
つよまる · tsuyomaru · JLPT N3 · verb-godan
to get strong
💪 強 tsuyo(i) = strong + まる = becomes: strong-becomes, on its own
強い (tsuyoi) means strong. The ending まる marks a change that happens by itself, as in 高まる (to rise) and 深まる (to deepen). Its partner 強める (tsuyomeru) is when someone makes a thing stronger.