減る
へる · heru · JLPT N3 · verb-godan
to decrease
💧 減 = 氵 water + 咸: water draining away, so the amount decreases
The water radical 氵 on the left hints at water level dropping. For the sound, heru is close to hair-u: hair that thins out over the years is hair that 減る, getting less and less.