To become complicated or intricate; to be elaborate or tangled (intransitive).
話が込み入ってきたので、もう一度整理して話しましょう。
The discussion has gotten complicated, so let's organize it and talk again.
この問題は法的にも込み入っているため、専門家に相談する必要がある。
This issue is legally complicated, so it's necessary to consult a specialist.
森の奥は道が込み入っていて迷いやすい。
The inner parts of the forest have tangled paths and are easy to get lost in.
Archaic: to push into; to be crowded or packed (rare/obsolete usage).
古文では人々が門に込み入ると書かれている。
In classical writing it is described that people pushed into the gate.