We don't have synonyms for king-at-arms yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are king-of-arms and king at arms.
(n) :
Alternative form of king-of-arms. [One of the three chief heralds of the College of Arms, designated as Garter (Principal King of Arms), Clarenceux (for England south of the Trent and Wales), and Norroy & Ulster (for England north of the Trent and Northern Ireland).]
(n) :
Alternative form of king-of-arms. [One of the three chief heralds of the College of Arms, designated as Garter (Principal King of Arms), Clarenceux (for England south of the Trent and Wales), and Norroy & Ulster (for England north of the Trent and Northern Ireland).]