オち

おち · ochi

verb 未然形

オち is the negative stem of オつ — to fall, to drop, to come down, to crash, to collapse, to cave in, to give way.

to set (of the sun or moon), to sink, to dip, to go down
to decrease (of popularity, quality, speed, sales, etc.), to fall, to drop, to go down, to decline, to deteriora

Classical Japanese — you’ll mostly meet it in older texts and set phrases

How it’s built

オつオち

Negative stem (未然形). Never used alone — it is the base for ない (not), れる/られる (passive), せる/させる (causative): 書か → 書かない.

オつ is a classical japanese conjugation, so it follows that pattern.