1. n. A device which separates a suspended, dissolved, or particulate matter from a fluid, solution, or other substance; any device that separates one substance from another.
2. n. Electronics or software that separates unwanted signals (for example noise) from wanted signals or that attenuates selected frequencies.
3. n. Any item, mechanism, device or procedure that acts to separate or isolate.
He runs an email filter to catch the junk mail.
4. n. (figurative) self-restraint in speech.
He's got no filter, and he's always offending people as a result.
5. n. (mathematics, order theory) A non-empty upper set (of a partially ordered set) which is closed under binary infima (a.k.a. meets).
The collection of cofinite subsets of ℝ is a filter under inclusion: it includes the intersection of every pair of its members, and includes every superset of every cofinite set.
If (1) the universal set (here, the set of natural numbers) were called a "large" set, (2) the superset of any "large" set were also a "large" set, and (3) the intersection of a pair of "large"
6. v. To sort, sift, or isolate.
7. v. To diffuse; to cause to be less concentrated or focused.
8. v. (intransitive) To pass through a filter or to act as though passing through a filter.
9. v. (intransitive) To move slowly or gradually; to come or go a few at a time.
10. v. (intransitive) To ride a motorcycle between lanes on a road
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