傾らか
なだらか · nadaraka · JLPT N2 · noun
gradual
傾 = tilt; なだらか = a slope that tilts gradually, not steeply
Standard spellings are 緩やか (gradual) and 平らか (level ground). 傾らか is non-standard, but 傾 (katamuku, tilt) fits the slope sense. Say na-da-ra-ka slowly, like a long, even slope.