The rinnard or roinnard is an Irish poetic form.
It has the following guidelines:
An example first:
Quatrain (or four-line) poem (or stanzas).
Six-syllable lines.
Two-syllable rhymes at the end of each line.
Rhyme scheme for each quatrain: abcb.
The “a” and “c” words consonate with the “b” words
Usually an alcill rhyme between lines three and four.
Note on aicill rhyme:
An aicill rhyme in this poem means that the final syllable of line three rhymes somewhere in line four (usually the middle).
Helpful Links
https://www.writersdigest.com/write-better-poetry/rinnard-poetic-forms
The Wombwell Rainbow 
This is going to be a bugger. There seem to be a lot of extras in this form, (the dunedh at the end, consonance) and I haven’t found a single example that sticks to its own rules…