What does hypothyroid mean?
Hypothyroid is a medical term describing an underactive thyroid gland or, more precisely, a deficiency of thyroid hormone. The resulting condition is known as hypothyroidism and may produce fatigue, weight gain, constipation, intolerance to cold, and other symptoms, although presentation and severity vary. As an adjective, hypothyroid is commonly used in phrases such as “hypothyroid symptoms” and “hypothyroid patient.” As a noun, it can refer to someone with the condition, though this usage is less common in modern medical writing, where “person with hypothyroidism” is often preferred. The term is especially useful in clinical contexts because it identifies a specific physiological pattern rather than merely describing general tiredness or weight change. It should not be confused with hyperthyroid, which denotes excessive thyroid hormone production and can cause many superficially similar but physiologically different symptoms.
Having an insufficient amount of thyroid hormone or an underactive thyroid gland.
"The patient was treated for a hypothyroid state caused by chronic thyroid inflammation."
Chiefly medical; it is more precise than the informal phrase “low thyroid.”
A person who has an underactive thyroid gland or insufficient thyroid hormone production.
"The clinician explained the treatment plan to the hypothyroid and arranged follow-up blood tests."
This noun use is less common in modern clinical writing; “person with hypothyroidism” may be preferred.
The plural is grammatically possible but uncommon; clinical writing generally uses “people with hypothyroidism.”
"The support group included hypothyroids from a wide range of age groups."
Hypothyroid points downward: the prefix hypo- means “under,” naming a thyroid that is producing too little hormone.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does hypothyroid come from?
The word combines the Greek prefix hypo-, meaning “under” or “below,” with thyroid, a term based on Greek thyreos, meaning “shield-shaped.” Thyroid itself was named for the shield-like form of the gland. The combined form developed in medical usage during the early 20th century, alongside the contrasting term hyperthyroid and the condition name hypothyroidism.
Related word forms
How hypothyroid is actually used
This is primarily a medical term. In general prose, “underactive thyroid” and “low thyroid” are often more immediately understandable. The noun use is relatively uncommon in contemporary clinical writing, where “person with hypothyroidism” may be preferred.
Easily confused with hypothyroid
Hypothyroid describes an underactive thyroid and reduced thyroid hormone production, whereas hyperthyroid describes an overactive thyroid and excess thyroid hormone production.
Thyroid can refer to the gland itself or generally to thyroid-related matters, while hypothyroid specifically denotes deficient thyroid function or a person who has it.