Observe. Remark, note, watch, heed, see, discover, attend, comment.
Ant. Overlook, misconceive, misunderstand.
Obsolete. Disused, ancient, neglected, antiquated, archaic, effete, past, old-fashioned, old, rare, obsolescent.
Ant. Fashionable, modern, current, customary, new, novel, extant.
Obstacle. Impediment, obstruction, difficulty, hindrance, barrier, check.
Ant. Course, proceeding, career, advancement, progress.
Obstinacy. Pertinacity, firmness, resoluteness, inflexibility, persistency, perverseness, contumacy.
Ant. Flexibility, docility, complaisance.
Obstinate. Perverse, obdurate, intractable, determined, stubborn, resolved, resolute, inflexible, unyielding, intractable, indomitable, unflinching, contumacious, decided, dogged, mulish, heady, headstrong, fixed, firm, immovable, opinionated, persistent, pertinacious, refractory, unconquerable.
Ant. Pliant, docile, submissive, dutiful, gentle, obedient, compliant, tractable, yielding, amenable, complaisant, irresolute, wavering, undecided, pliable, teachable.