Rod+Ros+and+Saga-Period+7


 * Rod/ros**- to gnaw

Robust- able to withstand adverse conditions

Erosion- the process of soil, rock, or land being gradually worn away

Corrosive- something that can destroy or damage by chemical reaction


 * Saga**- to perceive

Sagacious- having or showing good judgment

Sagacity- the quality of having good judgment

Presage- a sign that something bad will happen