Monstrous rhymes with:
ambidextrous, dextrous, disastrous, estrous, estrus, headmistress, lustrous, mistress, actress, ambidextrous, beatrice, buttress, citrus, dextrous, disastrous, estrous, estrus, fortress, headmistress, idolatrous, kontras, lustrous, mattress, mistress, nitrous, peatross, petrus, sentras, waitress, watrous
Monstrous sounds like:
master's, masters, masters', masterwork, masterworks, mastrich, mastrich's, mcdaris, mckitrick, mckittrick, mcwaters, mcwatters, megastores, meisters, mesothorax, minister's, ministers, ministers', ministries, ministry's, minstar's, misters, mistress, mistresses, mixtures, monasteries, monsters, moonstruck, mostar's, musketeers, musters, mysteries, mysterious