A made-up word with no true definition.
"Humorous fiction" is a funny story that is not true. It is made up.
Non-fiction is a story or book that is true, that really happened. Fiction is a story or book that is made up, that did not really happen.
Yes they are true in a Dictionary.
True
No, the opposite of a definition is certainly not always true. That would depend on the definitions and the meaning of the opposite.
To play by yourself
Yes: That relationship is part of the definition of a compound.
a pig
This is true by definition.
yes.
yes.