Definition of "Merthur"
Merthur
proper noun
(fandom slang) The ship of characters Merlin and Arthur Pendragon from the television series Merlin.
Quotations
Thousands of Merlin/Arthur stories were uploaded to www.fanfiction.net, in addition to other fan sites dedicated to 'Merthur', as the pairing became known.
2015, Philippa Semper, “'Camelot must come before all else': Fantasy and Family in the BBC Merlin”, in Gail Ashton, editor, Medieval Afterlives in Contemporary Culture, page 123
Given some viewers' objections to the presence of Gwen on Merlin, it is perhaps unsurprising that the most popular "ship" (fandom term for relationship) in the fandom is Merther—the undeniable connection between the young wizard and the monarch he serves so devotedly.
2019, Ebony Elizabeth Thomas, The Dark Fantastic: Race and the Imagination from Harry Potter to the Hunger Games, page 96