666 entries
AltF Lexicon lists 666 3-syllable words starting with O out of 3,715 entries under the letter. They are shown 60 to a page in dictionary order, each with its first definition, its syllable count and how common the word is.
Each of these applies on top of the current letter. The filter travels with you when you move to another letter in the strip above.
Looking for a pattern rather than a letter? Try the O word list, five-letter words or the 199 collections.