To go into or under a small, tight or difficult place (as a hole, under a rock, into dense brush, etc.); to go after s.t. that has gone into a hole or tight place [N-].
If transitive (N-, -in-) one is going after s.t.
I can't catch that chicken because it went under a bush that has many thorns.
If you can't manage to go after that chicken under the bush, have your dog go under it.
To stuff or insert s.t. into a hole, crack or crevice; to fill a hole with s.t. [The affixes ma-/pa-un always focus on the thing being inserted. The -an suffix can focus on either the object being inserted or the place where s.t. is being inserted].
Put some cement in this hole.