Posthumous rhymes with:
amos, animous, animus, anonymous, artemus, autonomous, bemis, blasphemous, brademas, cadmus, christmas, christmas', clackamas, deltadromeus, demas, demus, dermis, domas, enormous, epidermis, erasmus, famous, grimace, hippopotamus, humus, ignoramus, imus, infamous, isthmus, lemus, litmus, los-palmas, lummus, magnanimous, mandamus, mcamis, mccomas, monogamous, nostradamus, paramus, paulhamus, polhemus, polygamous, primus, promise, promus, pumice, pusillanimous, ramus, remus, seamus, shamas, shamus, st_thomas, synonymous, thalamus, thermos, thomas, trimas, ulmus, unanimous, varmus, venomous, warmus
Posthumous sounds like:
pakistan's, pakistanis, pastimes, pasting, picketing, pistons, pocketing, poseidon's, positioning, positions, postdating, posting, postings, pseudomonas, pseudonyms, psychodynamic