sub

a prefix occurring originally in loanwords from Latin ( subject; subtract; subvert; subsidy ); on this model, freely attached to elements of any origin and used with the meaning “under,” “below,” “beneath” ( subalpine; substratum ), “slightly,” “imperfectly,” “nearly” ( subcolumnar; subtropical ), “secondary,” “subordinate” ( subcommittee; subplot ).

Chemistry.

a prefix indicating a basic compound: subacetate; subcarbonate; subnitrate.

a prefix indicating that the element is present in a relatively small proportion, i.e., in a low oxidation state: subchloride; suboxide.

Also, su-, suc-, suf-, sug-, sum-, sup-, sur-, sus-.

Origin:
< Latin, combining form representing sub (preposition); akin to Greek hypó; see hypo-

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Based on the Random House Dictionary, © Random House, Inc. 2013.
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World English Dictionary

sub (sʌb)

—n
1.	subaltern subeditor submarine subordinate subscription substandard substitute See substratum short for several words beginning with sub-
2.	informal (Brit) Formal term: subsistence allowance an advance payment of wages or salary

—vb , subs, subbing, subbed
3.	(intr) to serve as a substitute
4.	informal (intr) to act as a substitute (for)
5.	informal (Brit) to grant or receive (an advance payment of wages or salary)
6.	informal (tr) short for subedit
7.	(tr) photog to apply a substratum to (a film or plate base)

sub.

—*abbreviation for*
1.	subeditor
2.	subito (in music)
3.	subscription
4.	substitute

sub-

—*prefix*
1.	situated under or beneath: subterranean
2.	secondary in rank; subordinate: subeditor
3.	falling short of; less than or imperfectly: subarctic; subhuman
4.	forming a subdivision or subordinate part of a whole: subcommittee
5.	in chemistry
	a. indicating that a compound contains a relatively small proportion of a specified element: suboxide
	b. indicating that a salt is basic salt: subacetate

[from Latin sub]

Collins English Dictionary - Complete & Unabridged 10th Edition
2009 © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009
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Etymonline

Word Origin & History

sub-

prefix of L. origin meaning "under," from L. preposition sub "under" (also "close to, up to, towards"), from a variant form (*(s)up-, perhaps representing *ex-upo-) of PIE base *upo- "from below," hence "turning upward, upward, up, up from under, over, beyond" (cf. Skt. upa "near, under, up to, on,"

Gk. hypo "under," Goth. iup, O.N., O.E. upp "up, upward," Hittite up-zi "rises"). Used as a prefix and in various combinations. The original meaning is now obscured in many words from Latin (suggest, suspect, subject, etc.); the prefix is active in Mod. Eng., however, sometimes meaning "subordinate" (as in subcontinent, first recorded 1863) or "inferior" (a sense first attested 1963). Many such words are transparent (e.g. subcommittee, 1610) and etymologies of their root words may be found under those headings. As a word of its own, sub is first recorded 1830, as a shortened form of substitute (originally of printer's substitutes). The verb in this sense is from 1853.

Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage

Medical Dictionary

sub- pref.

Below; under; beneath: subcutaneous.
Subordinate; secondary: subinfection.
Subdivision: subkingdom.
Less than completely or normally; nearly; almost: subfertility.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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American Heritage

Science Dictionary

sub-
A prefix that means "underneath or lower" (as in subsoil), "a subordinate or secondary part of something else" (as in subphylum.), or "less than completely" (as in subtropical.)

Slang Dictionary

sub definition

n.
a substitute. : I was a sub in the school system for a while.
in.
to serve as a temporary replacement. : I subbed for Mary in a couple of games.
n.
a submarine. : I was aboard a sub for twenty minutes—and that was at Disney World.
Go to submarine (sense 1). :
n.
a subscription, as to a magazine. : I got a sub to a computer magazine for my birthday.

Dictionary of American Slang and Colloquial Expressions by Richard A. Spears.Fourth Edition.
Copyright 2007. Published by McGraw Hill.
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FOLDOC

Computing Dictionary