Trimestry

Trimestry is an uncommon term that has appeared in English as a variant spelling of “trimester.” A trimester is a period of three months, used to divide a year or a gestational timeline into three roughly equal parts. The standard spelling in contemporary English is “trimester,” and "trimestry" is rarely used in modern writing.

Origins and form: The word derives from Latin tri- meaning three and mensis meaning month. The spelling “trimestry” likely reflects historical printing variations or regional usage rather than a distinct concept. Modern dictionaries generally list “trimester” as the standard form; “trimestry” is infrequently attested and often regarded as a misspelling or archaism.

Usage notes: In obstetrics, the three trimesters describe stages of pregnancy; in education, a trimester system divides the year into three terms. When encountering “trimestry” in older texts, it is typically interpreted as the same concept as “trimester” unless the context indicates otherwise. In contemporary writing, it is preferable to use “trimester” to avoid ambiguity.

See also: trimester, trimester system, academic calendar.