1. To stand erect
2. To rob, usually at gun point
3. When something long and narrow is raised above the surface, it sticks up.

1. When you use a gun or other weapon to rob people, banks, or stores, you stick them up. Hold up is the same as stick up.
2. When you put something, such as a picture, sign, or notice, in a place where people can see it, you stick it up.
3. When you push something inside a container or space that is long and narrow, you stick it up.