Almost without exception the armorial motto of the O'Dalaigh has been featured as "Deo et Regi Fidelis". However, the O'Dalaigh had used a Gaelic motto prior to the adoption of "Deo et Regi Fidelis" by those O'Dalaigh who wished to signify their loyalty to the reigning English monarchs.
Around the turn of the century, an Irish motto: "Laudir Agus Mir", meaning Swift and Strong, was found to have existed among the O'Dalaigh's of Galway and it's origin being very old. Indeed, "Laudir Agus Mir" is clearly descriptive of the O'Dalaigh crest whereas the usual one
"Deo Et Regi Fidelis", i.e. Faithful to my God and King is neither descriptive of the crest nor of the (mostly) disloyal family of O'Dalaigh's.
From "History of the O'Daly's, The Story of the Ancient Irish Sept, The Race of Dalach of Corca Adaimh" by Edmund Emmett O'Daly (Chicago, 1932).
O'Daly Marriage Stone