Real Dictionary

case containers
A case is a container that is specially designed to hold or protect something.
countable noun: A case is a suitcase.
countable noun: A case of wine or other alcoholic drink is a box containing a number of bottles, usually twelve, which is sold as a single unit.

case grammar term
countable noun: In the grammar of many languages, the case of a group such as a noun group or adjective group is the form it has which shows its relationship to other groups in the sentence.

case in American English 1
an example, instance, or occurrence
noun: an instance of the occurrence, existence, etc., of something

case in American English 2
a container, as a box, crate, chest, sheath, or folder
noun: an often small or portable container for enclosing something, as for carrying or safekeeping; receptacle
transitive verb: to put or enclose in a case; cover with a case

case in British English 1
noun: a single instance, occurrence, or example of something

case in British English 2
to put into or cover with a case
noun: a container, such as a box or chest

case instances and other abstract meanings
A particular case is a particular situation or incident, especially one that you are using as an individual example or instance of something.
If you say that someone is a sad case or a hopeless case, you mean that they are in a sad situation or a hopeless situation.
countable noun: A case is a person or their particular problem that a doctor, social worker, or other professional is dealing with.