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.
Another word (synonym) for the word "unpleasant" that starts with an "h" is "horrific". Or at least that is what I could think of.
updated
astamp
Atop.
Astonishing.
Amazing
advertise
"Deceiver" is another word for liar that starts with the letter A.