English Reference
noun

thesis

n.
US /ˈθisəs/ UK /θˈiːsɪs/ the·sis

  1. 01 B2 Upper Intermediate Academic

    the main idea or theory that you want to prove in a piece of writing or a speech.

    a proposition or statement maintained by argument; the central premise of a rhetorical or logical work.

    Simple

    The student's main thesis was that social media has changed how we make friends.

    In context

    The author's central thesis—that economic stability is a prerequisite for democratic growth—is supported by extensive historical data.

  2. 02 C2 Proficiency Technical Music

    the part of a rhythm that is not stressed, or the downward movement of a conductor's hand.

    the unstressed part of a poetic foot or a musical measure; also the downbeat in conducting.

    Simple

    The conductor marked the thesis of the bar with a clear downward motion.

    In context

    In classical prosody, the distinction between arsis and thesis is essential for understanding the rhythmic structure of the verse.

    downbeat
    arsis

Usage support thesis

Looking back today, Van Nieuwerburgh believes the paper's central thesis has held up.

Phys.org· 31 Aug 2026

Here’s my thesis, and I won’t soften it: we don’t own the moon, but we’re behaving as though we did, and that behavior has a name.

The Guardian· 31 Aug 2026

From Late Middle English thesis (“lowering of the voice”) and also borrowed directly from its etymon Latin thesis (“proposition, thesis; lowering of the voice”), from Ancient Greek θέσῐς (thésĭs, “arrangement, placement, setting; conclusion, position, thesis; lowering of the voice”), from τῐ́θημῐ (tĭ́thēmĭ, “to place, put, set; to put down in writing; to consider as, regard”) (ultimately from Proto-Indo-European *dʰeh₁- (“to do; to place, put”)) + -σῐς (-sĭs, suffix forming abstract nouns or nouns of action, process, or result). The English word is a doublet of deed. Sense 1.1 (“proposition or statement supported by arguments”) is adopted from antithesis. Sense 1.4 (“initial stage of reasoning”) was first used by the German philosopher Johann Gottlieb Fichte (1762–1814), and later applied to the dialectical method of his countryman, the philosopher Georg Wilhelm Friedrich Hegel (1770–1831). The plural form theses is borrowed from Latin thesēs, from Ancient Greek θέσεις (théseis).

Etymology adapted from Wiktionary, available under CC BY-SA 4.0.

This entry
Origin Ancient Greek θέσεις
Level B2 · Upper Intermediate
Frequency Common
Updated