o-

I. combining form or oo-

Etymology: Greek ōi-, ōio-, from ōion egg — more at egg

: egg

oidium

oology

specifically : ovum

oogenesis

oogonium

II. abbreviation

ortho-

* * *

o-¹

Chem.

an abridgment of ortho-.

o-²

var. of ob- before m: omission.

o-³

var. of oo-: oidium.

* * *

O- /ō-/ (chem)

prefix

Signifying ortho-

* * *

O¹ or o «oh», noun, plural O's or Os, o's, os, or oes.

1. the 15th letter of the English alphabet. There are two o's in Ohio.

2. any sound represented by this letter.

3. (used as a symbol) the 15th, or more usually the 14th, of a series (either I or J being omitted).

4. zero.

5. a mere nothing.

O² «oh», noun, plural O's.

anything shaped like the letter O: »

May we cram Within this wooden O [theater] the very casques That did affright the air at Agincourt? (Shakespeare).

O³ «oh», interjection, noun, plural O's.

–interj.

= oh! (Cf. ↑oh): »

O say, can you see, by the dawn's early light (Francis Scott Key).

–n.

an exclamation of oh: »

O's of admiration (Thackeray).

╂[Middle English O]

O⁴ «oh», noun, plural O's.

a person whose name begins with the prefix O'-: »

Ireland her O's, her Macs let Scotland boast (Henry Fielding).

o' «uh, oh», preposition.

1. of: »

man-o'-war, o'clock, will-o'-the-wisp.

2. on: »

Being knocked o' the head... (Richard Brinsley Sheridan).

O',

prefix. descendant, used as a prefix in Irish family names, as in O'Connell, »

O'Connor, O'Neil.

╂[< Irish ó descendant]

o-,

prefix. the form of ob- (Cf. ↑ob-) before m, as in omit.

o (no period),

1. ohm.

2. octavo.

o.,

an abbreviation for the following:

1. off.

2. officer.

3. order.

4. Baseball. outs or putouts (in scoring).

5. Pharmacy. pint (Latin, octarius or octavus).

O (no period),

1. oxygen (chemical element).

2. one of the four major blood types or groups widely used to determine blood compatibility in transfusions. A person with O type blood can receive blood of the O group only.

3. (in international flag code) man lost overboard.

O.,

an abbreviation for the following:

1. Ocean.

2. Octavo.

3. Ohio.

4. Old.

5. Ontario.

* * *

abbr. [used in combination] Chemistry ortho-

o-xylene