There are a total of 519 6-letter words starting with the letter 'o', and the number may vary in different dictionaries. You can specify the dictionary and order.

• office ₁₅
• others ₈
• object ₂₁
• orders ₇
• obtain ₁₀
• output ₁₁
• opened ₁₁
• occurs ₁₃
• origin ₉
• owners ₁₀
• offers ₁₂
• oxygen ₁₈
• option ₁₀
• oxford ₁₇
• orange ₉
• online ₉
• organs ₉
• offset ₁₂
• occupy ₁₈
• oliver ₉
• outlet ₈
• oldest ₈
• ounces ₁₁
• oppose ₁₂
• openly ₁₃
• outset ₇
• oxides ₁₄
• owning ₁₃
• optics ₁₂
• outfit ₁₀
• oceans ₁₀
• orient ₇
• onions ₈
• orally ₁₀
• oyster ₈
• outlay ₁₀
• onward ₁₁
• opaque ₁₉
• overly ₁₃
• orphan ₁₂
• obeyed ₁₂
• oblong ₁₃
• oracle ₁₀
• ocular ₁₁
• orator ₆
• orbits ₉
• ordeal ₈
• operas ₉
• olives ₁₁
• offend ₁₄
• occult ₁₄
• octave ₁₃
• obtuse ₁₀
• outlaw ₁₁
• oblige ₁₂
• odious ₈
• outing ₁₀
• orgasm ₁₁
• orchid ₁₂
• opioid ₁₀
• ornate ₇
• onsite ₇
• octavo ₁₃
• otitis ₆
• outcry ₁₂
• octane ₁₀
• opiate ₉
• opener ₁₀
• ousted ₈
• oiling ₁₀
• ordain ₈
• oblast ₁₀
• outage ₉
• oxalic ₁₇
• otters ₆
• oozing ₁₈
• oeuvre ₁₁
• oocyte ₁₁
• oedema ₁₀
• opined ₁₁
• olefin ₁₁
• ouster ₇
• oilers ₇
• opting ₁₂
• outrun ₉
• osmium ₁₃
• offing ₁₅
• olivet ₉
• ovules ₁₂
• oddity ₁₀
• osprey ₁₁
• oriole ₇
• ocelli ₁₁
• omelet ₁₀
• orgies ₈
• operon ₁₀
• oblate ₁₀
• optima ₁₂
• oleate ₇
• omnium ₁₄
• overdo ₁₁
• oilman ₁₁
• odours ₈
• ostium ₁₀
• obiter ₉
• outwit ₁₀
• oddest ₈
• oclock ₁₇
• orphic ₁₄
• oilier ₇
• oolite ₇
• oscars ₉
• offish ₁₄
• ostomy ₁₁
• objets ₁₈
• ornery ₉
• outdid ₉
• outbid ₁₁
• onsets ₇
• octets ₉
• oldies ₈
• opcode ₁₃
• opines ₁₀
• orrery ₈
• outran ₈
• ostler ₇
• oughly ₁₃
• orchis ₁₁
• ogling ₁₂
• oxalis ₁₄
• oilmen ₁₁
• obsess ₉
• overby ₁₄
• onrush ₁₀
• oximes ₁₆
• omened ₁₁
• orogen ₉
• ormolu ₁₁
• oocyst ₁₁
• oldman ₁₂
• octant ₁₀
• ondine ₇
• ointed ₇
• orison ₇
• ocelot ₁₀
• orated ₇
• okayed ₁₃
• oculus ₁₂
• orisha ₉
• orgone ₉
• oxcart ₁₆
• ozalid ₁₆
• oidium ₁₁
• offals ₁₃
• outers ₇
• ogival ₁₃
• oolong ₁₀
• ossify ₁₁
• octroi ₉
• ogress ₈
• oboist ₉
• osmose ₉
• offgas ₁₄
• ordure ₈
• oodles ₈
• otiose ₆
• osiers ₆
• ochres ₁₁
• oughts ₁₁
• otitic ₉
• osmund ₁₂
• owlish ₁₂
• obolus ₁₁
• orenda ₈
• ottava ₁₀
• oldish ₁₀
• overed ₁₁
• oxtail ₁₄
• orcein ₁₀
• ostial ₆

There are 519 6-letter words starting with the letter o in the well-known word game dictionary, in the Scrabble US (US/Canada/Thailand - TWL/NWL) dictionary, and in the Scrabble UK (International - SOWPODS/CSW) dictionary, and in the Words with Friends (WWF) dictionary.