You can c ('call') on most items to rename them which doesn't make a whole lot of sense to me. Most items automatically reveal certain features when used (i.e. applying or throwing a potion to discover its use) or are completely revealed when identified. In these cases, their names and descriptions are rewritten to describe them so you don't have to remember what they do.
Is there another reason for wanting to call something by a different name? As an example, can I
elbereth my swords for more power?