a. A reserve or substitute.
b. Computers A copy of a program or file that is stored separately from the original.
a. Support or backing.
b. Music A background accompaniment, as for a performer.
3. An overflow or accumulation caused by clogging or by a stoppage: a backup in the sink; a backup of traffic at the drawbridge.
Extra; standby: a backup pilot.
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2018 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.