A nice word beginning with a O?

optimistic

Answer

obdurate, obstinate, obfuscate, obedient, oasis, olive, obscure, occlude, ominous, omnipotent, omniscient, omnipresent, omnibus, omniverse, omnivore, oligosaccharide, occult, okapi, ocelot, otter, orangutan, obstreperous, olingo, oleaginous, ovoid, ovate, oocyte, oogamous, ooze, oops, oaf, oak, ochre, oriole, ogre, orc, orca, orotund, ozone, oxygen, oxidise, oxygenate, oxymoron, ox, osmium, otolaryngology, omen, omelette, ovule, ovulation, ovine, officious, opal, opulent, oxytocin, operculum