If "contain" means to hold something within:
* Release: To let something go free from confinement.
* Discharge: To release something from a confined space.
* Eject: To force something out.
* Empty: To remove all contents.
If "contain" means to limit or restrict:
* Expand: To increase in size or scope.
* Spread: To extend over a wider area.
* Diffuse: To spread out and become less concentrated.
* Emancipate: To free from restraint or control.
If "contain" means to include or comprise:
* Exclude: To leave something out.
* Omit: To leave something out.
* Lack: To be without something.
* Absent: To be missing.
To determine the most appropriate opposite, consider the specific meaning of "contain" in the context of your sentence.