Protohistory rhymes with:
history, history, mystery, blustery, celestory, history, mastery, mystery, upholstery, adultery, alimentary, artery, autery, battery, blustery, buttery, celestory, complimentary, contradictory, coterie, daughtery, directory, documentary, eatery, effrontery, factory, flattery, glittery, guattery, hattery, history, introductory, jittery, lottery, mastery, mcmurtrie, mystery, notary, olfactory, parliamentary, patrie, peremptory, perfunctory, petery, pottery, premonitory, raftery, rectory, refractory, rotary, rudimentary, sedimentary, slattery, splintery, supplementary, testamentary, trajectory, unsatisfactory, upholstery, valedictory, victory, watery
Protohistory sounds like:
predictor, protector, protester