optional
— Adjective
– English
～ possible but not necessary; left to personal choice
optionally
— Adverb
– English
～ in an optional manner; "this rule is applied optionally"
optometrist
— Noun
– English
～ a person skilled in testing for defects of vision in order to prescribe corrective glasses
optometry
— Noun
– English
～ the practice of an optometrist
opulence
— Noun
– English
～ wealth as evidenced by sumptuous living
opulent
— Adjective
– English
～ ostentatiously rich and superior in quality; "a princely sum"; "gilded dining rooms"; "these architecture magazines are full of the lush interiors of the rich and famous"
opulently
— Adverb
– English
～ in a sumptuous and opulent manner; "this government building is sumptuously appointed"
Opuntia cholla
— Noun
– English
～ arborescent cacti having very spiny cylindrical stem segments; southwestern United States and Mexico
Opuntia lindheimeri
— Noun
– English
～ cactus having yellow flowers and purple fruits
Opuntia
— Noun
– English
～ large genus of cactuses native to America: prickly pears
Opuntiales
— Noun
– English
～ coextensive with the family Cactaceae: cactuses
opus
— Noun
– English
～ a musical work that has been created; "the composition is written in four movements"
OPV
— Noun
– English
～ an oral vaccine (containing live but weakened poliovirus) that is given to provide immunity to poliomyelitis
or
— Noun
– English
～ a state in northwestern United States on the Pacific
OR circuit
— Noun
– English
～ a gate circuit in a computer that fires when any of its inputs fire
OR gate
— Noun
– English
～ a gate circuit in a computer that fires when any of its inputs fire
OR
— Noun
– English
～ a room in a hospital equipped for the performance of surgical operations; "great care is taken to keep the operating rooms aseptic"
or else
— Adverb
– English
～ in place of, or as an alternative to; "Felix became a herpetologist instead"; "alternatively we could buy a used car"
orach
— Noun
– English
～ any of various herbaceous plants of the genus Atriplex that thrive in deserts and salt marshes
orache
— Noun
– English
～ any of various herbaceous plants of the genus Atriplex that thrive in deserts and salt marshes