Is it legal to use poetry elements/sound devices as hints like "alliteration 3", "assonance 3", and "rhyme 3" in Codenames?
The rule is that clues must be about the meaning of the word. Alliteration, assonance, consonance, and rhyme are all about the construction and pronunciation of the word, and have nothing to do with the meaning of the word, they would very much fall under the quoted rule and be illegal clues.