tri·mes·ter (trī-mĕstər, trīmĕs′-)
1. A period or term of three months.
2. One of three terms into which an academic year is divided in some universities and colleges.
[French trimestre, from Latin trimēstris, trimēnstris, of three months : tri-, tri- + mēnsis, month; see mē-2 in the Appendix of Indo-European roots.]
tri·mestral (-trəl), tri·mestri·al (-trē-əl) adj.
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2019 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:
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