1'Donovan, John, and Eugene O'Curry. Letters Containing Information Relative to the Antiquities of the County of Clare, Collected during the Progress of the Ordnance Survey in 1839. Ed. Michael O'Flanagan. Bray, 1927.
O'Donovan is here quoting from the 14th-century text Cathreim Thoirdhealbhaigh, or Triumphs of Torlough. See more here. See O'Grady's translation here.
The full text of this poem, as translated by O'Donovan:

Let us give the title of King,
(Which will be of much fame
To the land which has chosen him)
To the valorous griffin [warrior]
The son of the fair-formed Donogh
Of the sealed secrets
Generous heir of generous Blood
The puissant Dermot of fortresses.
he is kind to the Church,
He is head over all,
The heart (centre) of the territories,
A tree under blossom.
Dermot of Dun Mor
The mild, lively, fierce,
Received the hostages
Through his wisdom and sword
His gracious smile and pomp (pride)
He exhibits with grace
And since he has commenced his career
His fame has spread afar
Momonia of Bards
Is his principality
Proclaim we him A King
Of his tribes with great joy.