preventer

pre·vent  (pr-vnt)

v. pre·vent·ed, pre·vent·ing, pre·vents

v.tr.

1. To keep from happening: took steps to prevent the strike.

2. To keep (someone) from doing something; impede: prevented us from winning.

3. Archaic To anticipate or counter in advance.

4. Archaic To come before; precede.

v.intr.

To present an obstacle: There will be a picnic if nothing prevents.

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[Middle English preventen, to anticipate, from Latin praevenre, praevent- : prae-, pre- + venre, to come; see g^w- in Indo-European roots.]

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pre·venta·bili·ty, pre·venti·bili·ty n.

pre·venta·ble, pre·venti·ble adj.

pre·venter n.

Synonyms: prevent, preclude, avert, obviate, forestall
These verbs mean to stop or hinder something from happening, especially by advance planning or action. Prevent implies anticipatory counteraction: "The surest way to prevent war is not to fear it" (John Randolph).
To preclude is to exclude the possibility of an event or action: "a tranquillity which . . . his wife's presence would have precluded" (John Henry Newman).
To avert is to ward off something about to happen: The pilot's quick thinking averted an accident.
Obviate implies that something, such as a difficulty, has been anticipated and disposed of effectively: "the objections . . . having . . . been obviated in the preceding chapter" (Joseph Butler).
Forestall usually suggests anticipatory measures taken to counteract, neutralize, or nullify the effects of something: We installed an alarm system to forestall break-ins.

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preventer [prɪˈvɛntə]

n

1. a person or thing that prevents

2. (Transport / Nautical Terms) Nautical a rope or other piece of gear rigged to prevent a sail from gybing