mnemonic

muistisääntö, muistikas

muistikas- Of or relating to mnemonics: the study of techniques for remembering anything more easily.
Anything (especially something in verbal form) used to help remember something.

To remember the colours of the rainbow, use the mnemonic "Richard of York gave battle in vain" (red, orange, yellow, green, blue, indigo, violet).

Mr Avery was a great believer in mnemonics; he had one for every possible aspect of flying – which was as good a way as any for student pilots to familiarise themselves with their new environment (..)