David Stifter wrote:

>> Instead I am
>> suggesting we have the s3 perfect of 'ad-gair' ('prosecutes, obtains,
>> forces onto someone'). Cf the later form (with 'do' for 'ro') at DIL
>> 56.50-51 'do-agair'.

> The prototonic variant of "ad-gair" has a /g/, written "c", e.g. "-acair".
> The spelling "do-agair" is only late and does not imply that there is a
> /gh/ present in the stem. Whereas /gh/ and /dh/ could be confused in later
> Irish, /d/ and /g/ could not.

I wonder then could the verb be 'aigid', which does have lenited 'g' and 
which also means 'prosecutes, sets going, forces onto someone'. 
(According to DIL A 110.22, the prototonic forms of 'ad-aig' are also 
supplied by 'aigid'.)

It would be s 3 present passive. We would expect 'ro-agar'. (We had to 
amend 'tomaid' to 'tomad' in the previous stanza). Note that there was 
'confusion both ways' between passive endings properly in -air and -ar 
in the Middle Iirsh period (Jackson, Aislinge Meic Con Glinne p 109).

This time, I suppose, we might have an impersonal present passive 'there 
is obtained by his vanity'. But I don't like it much. The first line 
leads me to expect a verb with Cormac as its subject. Perhaps 'Cormac is 
impelled by his vanity'. The grammatical structure is a bit 
impressionistic as a result, but I think it still works:

Cormac iar coraib cen chuibdius
ro-adair dia fheilius,
a lis cian ciarb’, olc in turas,
a lot ina leiges

Cormac after [= having extracted] a treaty without concord
Is driven by his vanity
in a distant dwelling - though the deed was evil,
[viz.] his [Tadg’s] wounding in his healing.

Does that fly?