'mythicise' originates from Modern English, formed from the adjective 'mythic' + the verb-forming suffix '-ise' (a variant of '-ize'), ultimately from Greek 'mythos', where 'mythos' meant 'story' or 'speech'.

'mythicise' changed from the adjective 'mythic' (itself from Old French/Latin adaptations of Greek 'mythos') combined with the productive English suffix '-ize/-ise' to create the verb 'mythicize' in Modern English; the spelling 'mythicise' is the British variant of the U.S. 'mythicize'.

Initially related forms meant 'pertaining to myth' (adjective); over time the verb form developed the meaning 'to make into or treat as a myth', including senses of idealizing or mythologizing.