Ob

UK: /ɔpj/ US: (ôb, ob; Russ. ôp)

WordReference Random House Unabridged Dictionary of American English © 2025

Ob  (ôb, ob; Russ. ôp), n. 

1. Place Names a river in the W Russian Federation in Asia, flowing NW to the Gulf of Ob. 2500 mi. (4025 km) long.
2. Place Names Gulf of, an inlet of the Arctic Ocean. ab. 500 mi. (800 km) long.

OB, 

1. Pathology Also, ob [Med.]
   • obstetrical.
   • obstetrician.
   • obstetrics.
2. Show Business off Broadway.
3. opening of books.
4. ordered back.

ob-, 

1. a prefix meaning "toward,'' "to,'' "on,'' "over,'' "against,'' orig. occurring in loanwords from Latin, but now used also, with the sense of "reversely,'' "inversely,'' to form Neo-Latin and English scientific terms:
   object;
   obligate;
   oblanceolate.

Also, o-, oc-, of-, op-. 

• Neo-Latin, Latin ob-
• Latin, representing ob (preposition); in some scientific terms,
• Old French)
• Middle English (

ob., 

1. he died;
   she died.
• Latin obiit
2. incidentally.
• Latin obiit
3. oboe.
4. Meteorology observation.

O.B., 

1. opening of books.
2. ordered back.
Also, O/B 

Collins Concise English Dictionary © HarperCollins Publishers::

Ob / ɔpj/ noun

1. a river in N central Russia, formed at Bisk by the confluence of the Biya and Katun Rivers and flowing generally north to the Gulf of Ob (an inlet of the Arctic Ocean): one of the largest rivers in the world, with a drainage basin of about 2 930 000 sq km (1 131 000 sq miles). Length: 3682 km (2287 miles)

WordReference Random House Learner's Dictionary of American English © 2025

ob-, prefix. 

1. ob- is attached to roots and means "toward,'' "to,'' "on,'' "over,'' "against'':
   object, obligate.

Collins Concise English Dictionary © HarperCollins Publishers::

OB abbreviation

1. Old Boy
2. outside broadcast

Collins Concise English Dictionary © HarperCollins Publishers::

ob- prefix

1. inverse or inversely: obovate

Etymology: from Old French, from Latin ob. In compound words of Latin origin, ob- (and oc-, of-, op-) indicates: to, towards (object); against (oppose); away from (obsolete); before (obstetric); down, over (obtect); for the sake of (obsecrate); and is used as an intensifier (oblong)

Collins Concise English Dictionary © HarperCollins Publishers::

ob. abbreviation

1. (on tombstones) obiit
2. obiter
3. oboe

Etymology: (for sense 1) Latin: he (or she) died; (for sense 2) Latin: incidentally; in passing