Both agraígí and agairt are forms of the Verb
agair, more specific
agair + ar (see:
https://www.teanglann.ie/en/fgb/agair)
agair = plead (thou)! (2nd person singular)
ná hagair = do not plead! (prefixed h is caused by ná)
agairt = to plead, pleading
agraím = I plead
d’agair mé = I begged
Different meaning with
ar (on): avenge
agair coir ar an bhfear = avenge a crime on the man!
ná hagair do dhíoltas orm = do not wreak thy vengeance on me!
agraígí = plead (ye)! (2nd person plural)
ná hagraígí, a fheara = don’t plead, ye men!
ná hagraígí bhur ndíoltas orm = don’t wreak ye yer vengeance on me!
So, agairt means revenge.