Gruesome
Grotesque
synonym for the word horrible that starts with the letter o is offensive, or obnoxious.
Another word for addition which starts with the letter N is New.
letter
Another word for water that starts with the letter 'O' is oxygen dihydrogen.
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Atop.
Amazing
Astonishing.
advertise
astamp
Another word (synonym) for the word "unpleasant" that starts with an "h" is "horrific". Or at least that is what I could think of.
Orator is another word for speaker.