A rhyming dictionary is a specialist dictionary designed for use in writing poetry and lyrics. In a rhyming dictionary, words are categorized into equivalence classes that consist of words which rhyme with one another. They will also typically support several different kinds of rhymes, and possibly also alliteration as well.
Because rhyming dictionaries are based on pronunciation, they are difficult to compile. Words and rhyming patterns change their pronunciation over time and between dialects. Rhyming dictionaries for Old English, Elizabethan poetry, or Standard English would have quite different content. Rhyming dictionaries are invaluable for historical linguistics – as they record pronunciation, they can be used to reconstruct pronunciation differences and similarities that are not necessarily reflected in spelling.
A simple reverse dictionary, which collates words starting from the end, provides a rough rhyming dictionary, to the extent that spelling follows pronunciation, but a precise rhyming dictionary reflects pronunciation, not spelling.