Trickle (in) can be defined as a slow, steady flow of liquid or gas. The crossword solution for this term is 'SEEP, ' which is defined as a slow, gradual leakage of liquid or gas. Seepage is often caused by the pressure of the liquid or gas pushing through a porous material, such as soil or rock. This type of slow, steady flow is often seen in nature, such as when water slowly seeps through the ground and into a stream or river.