i-adjective
miry; swampy; deep mud
Describes ground or a path that is deeply muddy, where one's feet sink in. The English gloss 'foundrous' is archaic and rare.
雨上がりの山道は泥深くて歩きにくい。
After the rain, the mountain path is miry and hard to walk on.
田んぼのあぜ道が泥深くなっている
The footpath between the rice paddies has become swampy.