Just to throw my 2 pence in
I think we have to be careful not to make things more confusing which I do think 'purge' does - it alludes to a situation which is not the case.
At the moment there is a complete distinction between stackfiles and objects in memory - the association is the same as that between a document when loaded into a word-processor and a document when being edited in the app. In this context the verb 'delete' is correct - it means delete the object from the environment just the same as selecting text in a document and pressing the delete key deletes that text from the document (and memory). There is no continually active link between the objects unserialized in memory and the source from which they were unserialized from.
The 'purge' verb suggests that this association is something stronger (to my mind at least) - i.e. you can purge a stack from memory and then get it back exactly as it was before the purge by opening the stackfile again but this is only the case if you save in between.
I think the problem here is that the distinction between objects and stackfiles is not being adequately articulated, or not being made clear enough, and (some) people are still thinking LiveCode operates in a similar way to HyperCard in terms of object storage - which it does not.
It is important to remember that HyperCard had (essentially) an object store - in the sense that on-disk representation and in-memory representation of objects was 'in-sync' - if you modified text in a field in HyperCard that change would be written back to disk when appropriate without any 'save' intervention. In this sense 'purge' makes sense because you are just saying 'I don't need this stuff in memory at the moment, so please release any memory related to it if you can'. In the current way LiveCode operates there can be no 'purge' operation in the same sense, since it does not work in the same way - i.e. there is nothing to fall back upon to revert the purge. [ Perhaps a succinct way to look at this is HyperCard was database-based, LiveCode is document-based ].
To my mind 'delete' is precisely the correct verb to represent the operation that you are performing in the way LiveCode currently works - delete operates on things in memory and gets rid of them, it has no relation at all to how the objects in memory might be preserved for opening in a later session.
Now, if LiveCode 'projects' were an object-store *then* there would be a distinction between purge and delete. 'purge' would mean just remove the in-memory representation of the object to save memory (because LiveCode could retrieve it when it was next needed 'exactly' as it was before the purge), and 'delete' would mean remove the object all together from the object-store and memory. (i.e. You could imagine the in-memory representation being a fast access cache for the information stored in the object-store on disk, thus 'purge' is akin to just purging data from a cache which isn't used right now).