godan verb (-mu), transitive verb
put away; stow away; tuck away; hoard
Emphasizes putting something completely away into a closed space (drawer, closet, box) so it is out of sight, often with a nuance of storing it for a long time or hiding it away. Can imply hoarding when used with large quantities.
使わない服をクローゼットにしまい込んだ。
I put away the clothes I don't use into the closet.
彼はお金をタンスに
He has a habit of stashing money away in the chest of drawers.