backronym

Short definition from Wiktionary

Noun

1. 1
   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.
2. 2
   A phrase which assigns a morpheme or word to each letter of a pre-existing acronym.

Verb

1. 1
   To create a backronym.