The phrase "dead as a dodo" refers to something that is extinct or obsolete. However, there are many other synonyms that can be used to convey the same message. For example, the phrase "extinct as the dinosaurs" is a common alternative. Other synonyms include "obsolete," "outdated," "archaic," "defunct," "extinguished," and "vanished." These words can be used in a variety of contexts, whether it be describing a technology that is no longer used or a fashion trend that has fallen out of style. No matter which synonym is used, the underlying message remains the same - that something has come to an end or is no longer relevant.