咲く
さく · saku · JLPT N5 · verb-godan
to bloom
🌸 saku sounds like sack: a sack of buds bursts open in bloom
咲 has the mouth radical 口; it originally meant to laugh, and a flower opening was described as the bud laughing. Same root idea as 笑. Link saku to sakura (桜), the cherry tree famous for blooming.