Criminal law is not a neat container. A crime is simply anything which is defined as being a criminal act within a given piece of legislation.

You can "decriminalise" something either by eliminating the entire piece of legislation, or by amending it to remove the criminal act within it. In the case of the latter, that leaves open the option of replacing it with other words that might indicate civil penalties. If that happens, that is still decriminalisation, and would be distinct from legalisation.