Modern invented blend of McKay (Scottish, 'son of Aodh') and Aiden (Irish, 'little fire').
Mckayden is a thoroughly contemporary American construction, born from the great naming revolution of the late 20th and early 21st centuries when parents began combining surname-style prefixes with the enormously popular "-ayden" suffix family. The McKay element derives from the Scottish Gaelic Mac Aoidh — "son of Aodh" — where Aodh (pronounced roughly "ee") was an ancient Celtic fire-deity name, making the underlying meaning something like "descendant of fire."
The McKay surname itself was borne by a Highland Scottish clan with a fierce reputation, and the name traveled to North America with Scottish and Scots-Irish immigrants, becoming embedded in Appalachian, Southern, and frontier naming traditions. The "-kayden" suffix burst into American naming consciousness in the 1990s and exploded through the 2000s, with Aiden, Jayden, Kayden, Brayden, and dozens of variants dominating birth registers. Mckayden represents the surname-prefix branch of this phenomenon, a sibling to names like Mckenzie and Mckinley repurposed as given names.
While traditionalists sometimes critique such constructions as rootless, they are in fact part of a genuine American naming tradition stretching back centuries — a creative, democratic impulse to forge new identities from available linguistic materials. Mckayden is almost exclusively used as a masculine given name in the United States, carrying the rugged surname sensibility of its Scottish roots fused with the breezy rhythmic flow of the -ayden generation.