To fall at high speed is this.
plummet
proof
genius
desperate
To need something with extreme urgency is to need it in this way.
currently
proof
plummet
desperately
A shelf or slab of stone, wood, or metal at the foot of a window or doorway is this.
current
sill
proof
frame
The evidence or argument that shows something is true.
sill
proof
genius
plummet
When a person is really very smart, we say the person is this.
plummet
sill
genius
desperate
Strong flows of air or water moving in a certain direction.
currents
plummet
desperate
genius