Slant
Slope
noun
A diagonal surface is a slant. A slope.
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
うちの私道は急斜面になってるので、上まで上がってくるにはスノータイヤがいります。
Our driveway has become a steep slope, so you need snow tires to get up it.