[on-lahyn, awn-]
operating under the direct control of, or connected to, a main computer.
connected by computer to one or more other computers or networks, as through a commercial electronic information service or the Internet.
of or denoting a business that transmits electronic information over telecommunications lines: an on-line bookstore.
available or operating on a computer or computer network: an on-line dictionary.
by means of or using a computer: on-line shopping.
Radio. (of a network) supplying affiliated stations with all or a substantial part of their programming.
Television. of or pertaining to the final editing of a videotaped program.
done or accomplished while in operation or active service: on-line maintenance.
located on major routes or rail lines: on-line industries.
with or through a computer, especially over a network.
Also, online, on line.
Compare off-line.


Dictionary.com Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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World English Dictionary
online or on-line (ˈɒnˌlaɪn)
1.  of, relating to, or concerned with a peripheral device that is directly connected to and controlled by the central processing unit of a computer
2.  of or relating to the internet: online shopping
3.  occurring as part of, or involving, a continuous sequence of operations, such as a production line
4.  while connected to a computer or the internet
on-line or on-line

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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Word Origin & History

in ref. to computers, "directly connected to a peripheral device," is attested from 1950 (originally as on-line).
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Science Dictionary
online   (ŏn'līn')  Pronunciation Key 
Connected to or accessible by means of a computer or computer network.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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American Heritage
Cultural Dictionary

online definition

A term referring to locations on or use of the Internet. The term can be used to refer to a specific location or Web page (“Our sales catalogues can be found online at — ”) or to a personal activity (“I went online to find the information you wanted.”)

The American Heritage® New Dictionary of Cultural Literacy, Third Edition
Copyright © 2005 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
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Example sentences
Online college courses have proliferated, and so have financial aid scams.
Many faculty members say it takes more time to develop and teach online courses
  than traditional ones.
Vote now and help our online audience pick the best pIt's your turn.
The author asked some of his acquaintances for permission to break into their
  online banking accounts.
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