An awdl was originally a poem of indeterminate length with a single end rhyme throughout, in a single meter. In the 12th century, The Poets of the Princes treated this iteration of the awdl as a poem in its own right, but by that time it was becoming more common for it to consist as one part of a larger poem, with different mono-rhymed sections each in a different meter, usually between 20-40 lines, almost always linked by the device called cyrch-gymeriad, which is to repeat either a whole word or sound between the end of one section and the beginning of the next, or by repeating the same word or sound at the beginning of each section. It became so that the entire poem was called the awdl, and the subsections were called caniadau in modern usage, or awdlau in older usage.

Then in the 14th c. the Englynion was introduced as a structural feature, either at the beginning of the awdl, between sections, or at its end. Sometimes all three.

So. What this means, is that when sources in English poetry say that the awdl is a family of 12 meters, using the principals of cynhanedd, this is what they’re referring to: an awdl is originally a long form poem of various sections/stanzas, each turning on one single end rhyme, and each using one metrical type (see below). With each meter type being complicated in they’re own right, it was something of a competitive feat for a poet of old to fit as many of the 24 official meters in one long Awdl.

In terms of the subsections, the stanzas, each line can be of different lengths with 8-10 syllables being average, though not strict. Each meter, or subtypes of awdl, each have their structure of shorter or longer lines and playing around with the general idea of the awdl end rhyme. Again, each stanza, subsection, of the awdle has no prescribed number of lines.

The tricky part about awdl, and really any old Welsh meter in general, is the use of cynghanedd. So far as I understand it, in any and every line the poet is to use one or more of the four cynhanedd, which can make things really, really technical. Leave it to the Welsh, right?

The 12 Awdl meters are as follows:

1. Rhupunt, (rhée-pint)
2. Cyhydedd fer (cuh-hée-dedd ver) (short equivalence rhyme)
3. Byr a thoddaid, (bir a thód-deyed) (short toddaid)
4. Clogyrnach (clog-ír-nach) 
5. Cyhydedd Naw Ban, (cuh-hée-dedd naw ban) 
6. Cyhydedd Hir, (cuh-hée-dedd heer) (long cyhydedd)
7. Toddaid, (todd-eyed) 
8. Gwawdodyn, (gwow-dód-in-heer) (gwad = poem)
9. Gwawdodyn hir, (gwow-dód-in heer) (long poem )
10. Hir a thoddaid, (heer-ah-thódd-eyed) (long stanza with toddaid)
11. Cyrch a chwta, (kirch-a-chóo-tah) (two rhyme a chwta)
12. Tawddgyrch cadwynog, (tówdd-girch ca-dóy-nog) (two rhyme chain)

 

For the curious, the rest of the 24 official Welsh meters are as follows:

The Englyn meters:

13. Englyn penfyr
14. Englyb milwr
15. Englyn unodl union’
16. Englyn unodl crwca
17. Englyn cyrch
18. Englyn proest dalgron
19. Englyn Heddfbroest
20. Englyn  proest gadwynog

 

The Cywydd meters:

21. Awdl gywydd (owdl gów-wid) (rhymed cywcdd)
22. Cywydd deuair hirion  (ców-idd dyé-ire héer-yon) (long-lined couplet)
23. Cywydd deuair fyrion  (ców-idd dyé-ire féer-yon) (short-lined couplet)
24. Cywydd llosgyrnog, (ców-idd llos-gr-nog)

 

 

Sources:

The Encyclopedia of Medieval Literature in Britain (Google Books Link)

Celtic Culture: A-Celti (Google Books Link)

The Cambridge History of Welsh Literature (Google Books Link)

The Mapping Medieval Chester Project (http://www.medievalchester.ac.uk/texts/welshmetre.html)