'archmediocrity' is a modern English coinage combining the prefix 'arch-' (from Greek 'archē' via Latin/Old French), meaning 'principal, chief, extreme', with 'mediocrity' (from Latin 'mediocris'), meaning 'moderate, ordinary'.

'arch-' entered English through Old French/Latin forms and has been used as an intensifying prefix (e.g. 'arch-rival'), while 'mediocrity' comes from Latin 'mediocris' via French into Middle English; the two elements were joined in modern English as a playful or ironic compound.

Individually, 'arch-' originally signified 'chief' or 'extreme' and 'mediocrity' meant 'moderateness' or 'ordinariness'; combined, the coinage shifted to an ironic sense of being 'chief among the mediocre' or 'remarkably mediocre.'