The spelling of the word "oneman" is quite simple once you break it down phonetically. Using IPA phonetic transcription, we can see that the "o" sounds like the "ah" in "father," the "n" is pronounced like "nn" (a nasal sound), and the "e" sounds like the "eh" in "pet." Finally, the "m" sounds like it does in "man." So, the full IPA transcription for "oneman" would be /ˈɑnɪmən/. So if you ever come across this word, now you know how to say it correctly.