Godan verb with 'mu' ending, Intransitive verb
to soak into; to sink into; to seep into; to permeate
雨は服にしみ込んだ。The rain soaked through my clothes. to sink into (one's mind); to be (deeply) ingrained; to be instilled; to be embedded; to be impressed
Also written 沁み込む【しみこむ】、浸み込む【しみこむ】、滲み込む【しみこむ】