押し込む
おしこむ · oshikomu · JLPT N1 · verb-godan
to push into
押す (push) + 込む (go into, crowd in) = push into; to crowd into
押し込む is built from 押す (to push) and 込む (to enter or go inside). Adding the two gives the sense of pushing something into a tight space.
押 — hand radical 扌 + 甲 (jiǎ, phonetic)
押 is a semantic-phonetic compound. The hand radical 扌 supplies the meaning of pressing or holding down with the hand, while 甲 gives the sound. From the literal sense of pressing, it extended to signing/sealing documents, mortgaging, and detaining — all involving an authoritative 'pressing' action.