What part of speech is mnemonic?

Answer 1

It is a noun and possibly an adjective. A mnemonic (noun form) is a memory aid. While it is redundant, you could refer to something as a mnemonic device. That would be using it as an adjective.

For instance, if you want to remember the notes on the bass clef, remember the sentence "Gold Buttons Dress Fine Actors." The first letters of each word are the music notes for each line.

Another example would be if you were making a speech and needed to remember your outline. One type of mnemonic would be to reduce each point into a single word. Then you take the first letter of each of those and either make them into a sentence using those words, or make those letters into a single word if you can.