The word "filtered" seems to be much more common than "filtrated". I know that these words derive from "to filter" and "to filtrate". What is the difference in meaning between these two verbs?

The context I have in mind is a mathematical one. Here the words "filtration" and "filter" have fixed and different meanings.

In addition, there is an invariant for certain objects which are endowed with a filtration (technically this isn't accurate but let's suppose so). This invariant is called "filtrated K-theory" by several people. Yet, some people insist that it should be called "filtered K-theory" because filtrated is hardly a word or at least sounds weird and artificial. Can native speakers confirm this, or would you go for the more logical(?) "filtrated"?

  • 1
    Once upon a time, I got a bachelor's degree in mathematics, but I've never heard of "filtration" having any special meaning. Or even much of a meaning at all. :/
    – Marthaª
    Commented Mar 14, 2011 at 19:47
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    @Martha: some for me. The Wikipedia page about it easy to read, but the word was never introduced to me in math classes at university.
    – F'x
    Commented Mar 14, 2011 at 19:49
  • Thanks, @F'x. For completeness, filter on wikipedia.
    – Rasmus
    Commented Mar 14, 2011 at 19:59

4 Answers 4


The meanings of jargon terms often have essentially nothing to do with the meanings of the English words they're made from. Nowhere is this more the case than in mathematics.

I would use whichever term seems better established—regardless of whether it sounds artificial to native English speakers who aren't mathematicians—so as to give the reader the best possible chance to figure out what I'm talking about.

Updated: I should just answer your question. To my ear, there is a verb filter, and a count noun filter. There is also a non-count noun filtration. (You can count coffee filters, but the filtration of water through coffee grounds isn't something you can count.) So already the mathematical use of filtration as a count noun ("a filtration") differs from the everyday use.

I am pretty sure I never heard the verb filtrate used in everyday English until I started searching for such uses just now. A Google search for filtrated hits mainly dictionary sites. At the moment, the first non-dictionary hit is a link to this question! I can confirm that to my ear, it's hardly a word, and it sounds weird and artificial. Filtered sounds much nicer to me. It is an actual common, everyday word (and, correspondingly, gets hundreds of times as many Google hits).

  • thanks, I agree. In the case at hand, I feel that the terminology is not yet fully established. That's what makes it interesting for me.
    – Rasmus
    Commented Mar 14, 2011 at 20:30

The main meaning of filter is derived from the field of chemistry: “to pass (a liquid, gas, light, or sound) through a device to remove unwanted”. It this meaning, filtrate and filter are absolutely synonymous.

In specific uses, such as “people filtered out of the room” or “news began to filter in from the hospital”, it sounds rather weird to use filtrate.

Finally, as a side node, a filtrate (noun) is the name of a liquid coming out of a filter (basically, the filtered or filtrated liquid is a filtrate).

Edit: OK, so there was a second question… which I don't know how to address! I'm not a native speaker, but “filtrated” doesn't sound to weird to me :)

  • What is your opinion on my second question?
    – Rasmus
    Commented Mar 14, 2011 at 19:59
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    Not being a mathematician by trade, I cannot comment on your second question. However, your suggestion seems more logical.
    – UserID
    Commented Mar 14, 2011 at 20:14
  • +1 As a verb, filtrate has a very specific meaning: to remove by passing through a filter. The verb filter as this meaning too, but it can also simply mean pass through or flow slowly.
    – ghoppe
    Commented Jun 14, 2011 at 17:52
  • No no, filtrate and filter are NOT synonymous, unless you specify them as verbs. At that point, I find filtrate only in my 'word book, not in Webster's collegiate 1956, and only as an aside in Webster's unabridged 1959 Commented Jun 14, 2011 at 22:04

To answer your second question... by that point you're creating technical jargon, so it'll just be whatever people decide on it being. "filtrated K-theory" seems more common than "filtered K-theory", according to Google, so that seems to be winning out, currently.


My first response is one of revulsion to hear 'filtrated', as I presume the intent is to say 'filtered'. In a chemical context, 'filtrate' is a noun, meaning what comes out of the filter. The use of 'filtrated' immediately makes me suspicious of the speaker's credentials.

My old Webster's lists under the verb filter ... 'n filter, cf filtrate'. Go figure.

But in some other field, there might be a process something like 'infiltration', where filtrated describes some subtle property of the thing, and not simply that it has been filtered. That seems to be the case with your 'filtrated k theory'.

To answer which is the correct term in the context of 'filtered k theory' requires first that you know what 'filtered k theory' actually is. Are the k groups somehow filtered? Is there good reason to describe them as 'filtrated'?

Using a google search to choose the most often found version is bad for science.

  • ok, I read the filtrated wiki, thanks, @Fx. In this context, filtered and hence filtrated have meanings specific to algebra, and it would be the use of the term 'filtered k theory' that would invoke distrust, as it seems the correct term is 'filtrated'. Commented Jun 14, 2011 at 22:15

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