Declan
[ˈdɛklən]Meaning
anglicized form of Irish Deaglán, of unknown meaning
Background Story
Declan is the anglicized form of the Irish name Deaglán, itself from Old Irish Declán. The meaning is unknown, though it likely begins with the Old Irish prefix dag, "good". The name is recorded in Old Irish, with Deaglán as a variant and Declán as a same-spelling form. In America it received boosts in popularity from main characters in the movies The Jackal (1997) and Leap Year (2010).
Temperament

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