The term 'permeate gradually' can be summarized by the crossword solution 'SEEP'. Seepage is the process of a liquid slowly passing through a porous material, such as soil or rock. This process is often used to describe the gradual infiltration of water into the ground, but it can also be used to describe the slow diffusion of a gas or other substance. In this context, permeate gradually could refer to a liquid or gas slowly diffusing through a material.