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dilate

/ˈdaɪleɪt//daɪˈleɪt/·verb
to make or become wider, especially an opening
Fig. 1 — A camera's iris sits almost shut, just a pinhole at the centre.
01Definition

To dilate is to widen — most often an opening: pupils dilate in the dark, blood vessels dilate with heat, a valve dilates to let more through. From Latin dīlātāre, 'to spread wide' (latus, 'wide', also behind latitude), it is a formal, faintly clinical word. It has a second, literary life too: to dilate on a subject is to speak or write about it at length, spreading your words wide. It works both ways — drops dilate the pupil, and the pupil dilates. Its opposite is to constrict.

02In use
  • iIn the dark, the pupils dilate to gather what little light there is.
  • iiThe drug dilates the blood vessels, so more blood can flow and the pressure eases.
  • iiiShe would dilate on the smallest point for an hour, long after everyone had grasped it.
03Collocations
  • pupils dilate
  • dilate the blood vessels
  • dilate on a subject
  • fully dilated
  • dilate with heat

Family dilation (noun) · dilatation (noun) · dilated (adjective)

04Relations

=widen, expand, enlarge, distend, open

≠constrict, contract, narrow

05Compared
PairThe difference
dilate vs constrictthe channel is squeezed narrower and less gets through → constrict; the opening widens and more gets through → dilate.
dilate vs contractthe whole thing draws inward, smaller or tighter → contract; an opening widens from the middle out → dilate.
dilate vs dilutean opening widens (pupils, vessels) → dilate; a liquid or strength is thinned by adding more → dilute.
dilate vs narrowan opening widens, in formal or clinical register → dilate; width is lost, in everyday register → narrow.
06TOEFL & IELTS

Dilate is a formal, technical verb — reserve it for openings that widen (pupils, vessels, valves) and for physics ('metals dilate with heat'), not for general widening, where widen or expand fit. Two facts examiners like: the noun is dilation in general use but dilatation in medicine; and 'dilate on/upon a topic' means to discuss it at length — a rare, formal sense worth recognising in older academic prose.

07Asked
How do you pronounce 'dilate' — DIE-late or di-LATE?
Both are correct. Americans usually say DIE-late, stressing the first syllable — /ˈdaɪleɪt/. British speakers more often say di-LATE, stressing the second — /daɪˈleɪt/. Either is accepted; what you should avoid is a short first vowel ('dill-ate') — the 'di' always sounds like 'dye'.
What does dilate mean?
To dilate is to make or become wider, especially an opening: pupils dilate, blood vessels dilate, a valve dilates. It is the formal, often medical word for an aperture enlarging — as the scene above shows with a camera iris opening from a pinhole to a wide, round aperture from the centre out.
What does 'dilate on' or 'dilate upon' a subject mean?
It means to speak or write about something at length — to expand on it. 'He dilated on the theme for a full hour.' It is a formal, slightly old-fashioned sense, drawn from the word's root idea of spreading wide, and you are most likely to meet it in literary or nineteenth-century prose.
What is the opposite of dilate?
Constrict — to narrow or squeeze an opening. Pupils dilate in the dark and constrict in bright light; vessels dilate with heat and constrict with cold. 'Contract' and 'narrow' are looser opposites, but constrict is the exact partner, since it too is about an opening being made smaller.
Dilation or dilatation — which is correct?
Both are real words for the act of dilating; the choice is regional and by field. Dilation is the everyday and American spelling ('dilation of the pupils'). Dilatation is older and chiefly British and medical ('dilatation of the aorta'). They mean the same thing — pick one and stay consistent.
Is dilate only a medical word?
No, though medicine is its busiest home. It is also a physics term — metals dilate as they heat — and it keeps the literary 'dilate on a subject' sense. What it is not is a casual synonym for 'get wider': for a road or a gap you would say widen, and for size or scope, expand. Dilate stays formal and tends to describe openings.