Modern spelling of Braiden or Braden, usually traced to Irish surname roots.
Braidyn is a creative orthographic variant of Brayden, which itself descends from the Irish surname Ó Bradáin — "descendant of Bradán," where bradán is the Old Irish word for salmon. The salmon occupied a position of profound mythological importance in Celtic tradition: in Irish legend, the Salmon of Knowledge (An Bradán Feasa) dwelt in the Well of Segais, eating hazelnuts that fell from the nine sacred hazel trees ringing the well. The hero Fionn mac Cumhaill gained all the wisdom of the world by accidentally tasting the juice of this salmon as he cooked it for the druid Finnegas.
To carry a name rooted in bradán is to carry, however distantly, a trace of that ancient mythos of wisdom sought and earned. The Brayden family of names crossed into popular usage in the United States during the 1990s and 2000s, riding the wave of Irish-influenced surnames-as-first-names that also lifted Brady, Brennan, and Flynn into the mainstream. The variant spellings — Brayden, Braden, Braiden, and Braidyn — reflect the American tendency to personalize names orthographically, distinguishing one child's name from another's through spelling rather than sound.
Braidyn in particular gives the name a visual distinctiveness, the internal "ai" digraph lending it a slightly more ornate character on the page. It remains firmly a child of its era while carrying underneath it that quiet Celtic heritage of rivers, silver fish, and hard-won knowledge.