I wrote: 
>>Nicon bia ach teach bachlach uait

Neil McLeod wrote: 
>With Old/Mid Ir 'acht' spread over two lines, read
>  'acht each-bachlach', or plural 'each-bachlach[u]'?
>(In the MS someone has 'corrected' it below the line to nom.? pl.
>Cf DIL E 28.43.

Thanks, Neil,
  I see the above  reference in DIL, which quotes our text as a single example of the 
compound 'echbachlach', with a question mark after it.   

   I thought it might be 'teach bachlaich' ..  translating 'a house of a servant', 'a servant's 
DIL T 97.35 gives three examples of 'tech' used to mean  "family, line". 
  Bachlaich could be genitive singular of o stem masculine  'bachlach...rustic, servant, 
labourer, serf, ignorant person'.  Meaning that Mongan's  line would have the same status as 
the descendants of his servants.  

   'Teach' can be accusative singular, so that would fit after 'ach'.
'Ach' is Modern Irish, but 'Ach, see acht' is listed as a headword in DIL. 
This made me think 'ach' might be an acceptable Middle Irish variant. 

   Am I forgetting something here?   Liz