The crossword solution for the term 'penetrate, with 'IN'' is SOAK. To penetrate something with 'IN' means to SOAK it IN a liquid or other substance. This could be used to describe a variety of activities, such as soaking a cloth IN water to clean it, or soaking a piece of wood IN a preservative to protect it from rot. IN general, to penetrate something with 'IN' means to submerge it IN a liquid or other substance.