Learn what the dictionary tells you about words.

Get Started Now!

Some compound words (like bus rapid transit, dog whistle, or identity theft) don’t appear on the drop-down list when you enter them into the search window. If a compound term doesn’t appear in the drop-down list, try entering the term into the search window and then hit the search button (instead of the “enter” key). Alternatively, begin searches for compound terms with a quotation mark.



The Usage Panel is a group of nearly 200 prominent scholars, creative writers, journalists, diplomats, and others in occupations requiring mastery of language. The Panelists are surveyed annually to gauge the acceptability of particular usages and grammatical constructions.

The Panelists



Go to our Crossword Puzzle Solver and type in the letters that you know, and the Solver will produce a list of possible solutions.



The new American Heritage Dictionary app is now available for iOS and Android.



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:

Indo-European Roots

Semitic Roots

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.


See word lists from the best-selling 100 Words Series!

Find out more!



Check out the Dictionary Society of North America at

par·al·lel (părə-lĕl)
1. Being an equal distance apart everywhere: dancers in two parallel rows. See Usage Note at absolute.
2. Mathematics
a. Of, relating to, or designating two or more straight coplanar lines that do not intersect.
b. Of, relating to, or designating two or more planes that do not intersect.
c. Of, relating to, or designating a line and a plane that do not intersect.
d. Of, relating to, or designating curves or surfaces everywhere equidistant.
a. Having comparable parts, analogous aspects, or readily recognized similarities: the parallel lives of two contemporaries.
b. Having the same tendency or direction: parallel motives and aims.
4. Grammar Having identical or equivalent syntactic constructions in corresponding clauses or phrases.
5. Music
a. Moving in the same direction at a fixed interval: parallel motion; parallel fifths.
b. Having the same tonic. Used of scales and keys: C minor is the parallel minor scale of C major.
6. Electronics Denoting a circuit or part of a circuit connected in parallel.
7. Computers
a. Of or relating to the simultaneous transmission of all the bits of a byte over separate wires: a parallel port; a parallel interface.
b. Of or relating to the simultaneous performance of multiple operations: parallel processing.
In a parallel relationship or manner: a road and a railway that run parallel.
1. Mathematics One of a set of parallel geometric figures, such as lines or planes.
a. One that closely resembles or is analogous to another: a unique event, without parallel in history.
b. A comparison indicating likeness; an analogy.
3. The condition of being parallel; near similarity or exact agreement in particulars; parallelism.
4. Any of the imaginary lines representing degrees of latitude that encircle the earth parallel to the plane of the equator.
5. Printing A sign indicating material referred to in a note or reference.
6. Electronics An arrangement of components in a circuit that splits the current into two or more paths. Used chiefly in the phrase in parallel.
tr.v. par·al·leled, par·al·lel·ing, par·al·lels also par·al·lelled or par·al·lel·ling
1. To make or place parallel to something else: paralleled the ditch to the highway.
2. To be or extend parallel to: a trail that parallels the crater rim.
3. To be similar or analogous to: claimed that fetal development parallels the evolution of the species.
4. To be or provide an equal for; match.
5. To show to be analogous; compare or liken: critics who have paralleled the novel's plot to an ancient myth.

[Latin parallēlus, from Greek parallēlos : para-, beside; see PARA-1 + allēlōn, of one another (from allos, other; see al-1 in the Appendix of Indo-European roots).]

The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2018 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

This website is best viewed in Chrome, Firefox, Microsoft Edge, or Safari. Some characters in pronunciations and etymologies cannot be displayed properly in Internet Explorer.