tri·​io·​do·​thy·​ro·​nine ˌtrī-ˌī-ə-dō-ˈthī-rə-ˌnēn How to pronounce triiodothyronine (audio)
: an iodine-containing hormone C15H12I3NO4 that is an amino acid derived from thyroxine

called also T3

Examples of triiodothyronine in a Sentence

Recent Examples on the Web The hormones that the thyroid gland makes — triiodothyronine, or T3, and thyroxine, or T4 — affect all aspects of your metabolism. Mayo Clinic News Network,, 4 Oct. 2019 Your thyroid produces hormones like thyroxine and triiodothyronine, which influence many of your body’s systems, according to the Mayo Clinic. Zahra Barnes, SELF, 16 Jan. 2018

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'triiodothyronine.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

Word History


tri- + iod- + thyronine an amino acid of which thyroxine is a derivative

First Known Use

1952, in the meaning defined above

Time Traveler
The first known use of triiodothyronine was in 1952

Dictionary Entries Near triiodothyronine

Cite this Entry

“Triiodothyronine.” Dictionary, Merriam-Webster, Accessed 4 Oct. 2023.

Medical Definition


tri·​io·​do·​thy·​ro·​nine ˌtrī-ˌī-əd-ō-ˈthī-rə-ˌnēn How to pronounce triiodothyronine (audio)
: a crystalline iodine-containing hormone C15H12I3NO4 that is an amino acid derived from thyroxine and is used especially in the form of its soluble sodium salt C15H11I3NNaO4 in the treatment of hypothyroidism and metabolic insufficiency

called also liothyronine, T3

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