Reading my earlier post above, I realise it wasn’t quite right. Assonance is typically using rhymes where only the vowel sounds repeat, like ‘leaves’ and ‘green’, and consonance is using rhymes where only consonant letters repeat, like ‘wind’ and ‘hand’ (or indeed ‘be slain’ and ‘agen’). Rap lyrics tend to exploit assonance (ironically presumably), but surely folk song is rather more subtle.