Dilate and dilute look and sound alike but do different jobs in different sciences. To dilate is to widen — especially an opening: pupils dilate in the dark, blood vessels dilate with heat. To dilute is to thin a liquid by adding more, usually water, so its strength drops: you dilute an acid or a cordial. One vowel apart: dilate spreads an opening wide; dilute spreads a substance thin.
The resemblance is an accident of Latin. Dilate comes from dilatare, 'to spread wide' — the same latus ('wide') that gives latitude. Dilute comes from diluere, 'to wash away', and keeps that sense of strength draining out as water goes in. Both spread something — but dilate spreads an opening until more can pass through, while dilute spreads a substance through so much liquid that its force fades. Anatomy and physics dilate; chemistry dilutes.
dilate
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.
dilute
To dilute is to weaken by spreading thin — classically by adding water, so a strong solution becomes mild. From the Latin diluere, 'to wash away', it keeps that sense of strength draining out: dilute the acid, dilute the juice. Figuratively, anything concentrated can be diluted — a message, a brand, a share of power — when it is stretched across too much. It is the opposite of saturate: where one packs more in, the other thins it out until little force remains.
| dilate | dilute | |
|---|---|---|
| Meaning | widen, especially an opening | thin a liquid; weaken |
| Home field | anatomy, physics (pupils, vessels) | chemistry, cooking (solutions) |
| What changes | the opening gets bigger | the concentration gets lower |
| Often with | pupils, blood vessels, fully dilated | a solution, heavily diluted, dilute the impact |
| Opposite | constrict | concentrate |
| Noun | dilation (medicine: dilatation) | dilution |
One scene widens a hole; the other thins a colour. Dilate is the camera iris drawing open from pinhole to full aperture — the opening grows so more gets through. Dilute is the drop of colour blooming through a beaker until it is too pale to matter — the amount is unchanged but spread too thin. So: if a gap, pupil, or vessel is getting wider, it dilates; if a liquid (or a message) is getting weaker by being spread out, it is diluted.
dilate
- iIn dim light the pupils dilate to let more of the scene in.
- iiA hot bath makes blood vessels dilate, which is why the skin flushes.
- iiiThe surgeon waited for the valve to dilate fully before proceeding.
dilute
- iDilute the concentrate with three parts water before serving.
- iiEach new round of shares diluted the founders' control of the company.
- iiiAdding too many side plots dilutes the impact of the main story.
The slip is nearly always dilate written for dilute or the reverse — one vowel, two sciences. A useful tell: dilate takes openings as its object or subject (pupil, vessel, cervix), while dilute takes liquids and figurative strength (solution, acid, message, power). Their opposites differ too: what dilates can constrict; what is diluted can be concentrated.
TOEFL science passages keep them apart by field: biology dilates (pupils, vessels, vasodilation) and chemistry dilutes (a dilute acid, serial dilution). In IELTS Writing the figurative dilute is the prize — 'this dilutes the impact of the policy'. Watch the nouns: dilution for the liquid, dilation for the opening (medicine also uses dilatation). Spelling is the exam trap: one vowel — a for wide, u for washed out.