Deylan is likely a modern variant of Dylan, the Welsh name associated with the sea or great tide.
Deylan is a modern respelling of Dylan, a name that flows directly from the Welsh poetic tradition. The original Dylan — Dylon in some early manuscripts — appears in the Mabinogion, the great cycle of Welsh mythology collected in the 12th and 13th centuries. Dylan ail Don, 'Dylan son of Wave,' is a sea deity born of the virgin Math's magical testing, a child so at home in the ocean that he slips into it the moment he is baptized and becomes indistinguishable from the sea itself.
The name almost certainly derives from the Welsh dy (great) and llanw (tide or flood), making it one of the most evocative nature names in the Celtic tradition — not a name about the sea so much as a name that is the sea. Dylan rose dramatically in the English-speaking world after Robert Zimmerman adopted it as his stage name in honor of the Welsh poet Dylan Thomas, whose 1953 death had made him a tragic romantic figure for the Beat generation. Bob Dylan transformed the name from a Welsh obscurity into a global emblem of artistic independence and countercultural cool.
By the 1990s and 2000s, Dylan had become mainstream enough that variant spellings like Deylan, Dylen, and Dillan began appearing among parents who wanted the name's sonic and cultural resonance while giving their child something visually more singular. Deylan carries all of Dylan's oceanic poetry and mid-century cool in a form that feels freshly individualized.