All, I am just curious why 'monotonous' is spelled as mo·not·o·nous and not as mono.tonus following the Greek origin of the word as mono + tone. Mono and tone could be spelled alone and actually they constitute the word monotonous. Thanks
I think you are asking why this word is spelt with -ous rather than with -us. In English, -ous is the usual offshoot of Latin -us in words borrowed via Old French; the development is -us > -eux > -ous. Later, this spelling is adopted also for words taken directly from Latin or Greek. We have glorious, copious, generous and lots more.