油底壳

oil sump

(equivalent to 的 as possessive particle)

background / bottom / base / end (of the month, year etc) / remnants / (math.) radix / base

oil / fat / grease / petroleum / to apply tung oil, paint or varnish / oily / greasy / glib / cunning

shell / carapace / crust (earth's crust etc) / also pr. [ke2]