ground-breaking, open up farmland
JLPT1 G7 S16 F5000
貇 combines 艮 (adhere) with 豸 animal that ambles along the ground → teeth of a sharp-toothed beast adhering to an object or to the piece of food being gnawed → gnaw. 墾 is as per 貇# (adhere) + 土 earth → agricultural tool adhering to the soil in *cultivation*.
[Full Kanji Etymology List]