regiment, party, company, squad
JLPT1 G4 S12 F605
An abbreviated form# of 遂 (heavy object) + 阜 piled earth → heavy pile of earth that collapses to the ground (compare 隋). *Unit* is either via association (e.g. a collapsed earthen structure perceived as the ruins of a single unit) or borrowing → *corps* (← a unit of soldiers).
[Full Kanji Etymology List]