backronym

A word that is originally not an acronym but is turned into one by devising a full form for it, sometimes as a folk etymology, sometimes as a contrived acronym to name a new organization, proposal, or other entity.

[T]he phenomenon has been dubbed STEVE, a backronym that matches the name originally given by aurora watchers. (STEVE is short for "Strong Thermal Emission Velocity Enhancement.")

These reverse-engineered acronyms, or “backronyms,” are inescapable on Capitol Hill. Two of the biggest laws of the past few years were the CARES Act, for pandemic relief, and the CHIPS for America Act, for semiconductor manufacturing. […] Yet congressional backronyms have been on the rise for years: I wrote a computer program to check legislation titles for acronyms that spell out complete words, and found that roughly 10 percent of bills and resolutions introduced over the past two years have had backronym names—up from about one in 20 a decade ago and less than 1 percent in the late 1990s.

A phrase which assigns a morpheme or word to each letter of a pre-existing acronym.

To create a backronym.