transmission, a gearbox (a mechanical assembly of gears that changes the torque and speed of shaft rotations)

Rube Goldberg machine

transporter, transportation machine.

underground water

experimental device; experimental equipment

underground line, specifically an underground cable or wire

(AmE) subway; (BrE) underground; (BrE) tube

七七日: the forty-ninth day after a person dies; the Buddhist memorial service that occurs forty-nine days after a person dies

(onomatopoeia, slang) sexy

日日: day by day