Dec 17- Thoddaid, A basic form, a couplet with 10 syllables followed by 9 syllables. A short modified form has 10 syllables followed by 6 syllables. Typical form as follows: xxxxxxxxbxx, xxxxbxxxa.

The Thoddaid is a basic Celtic form

Ten syllables tell at first then nine.
 
Assonance hosts a poet’s shell
Alliterate well to make it fine.