I've come across the term annular ring in parentheses following washer in my calculus textbook: "has the shape of a washer (an annular ring)". The definition of the word "annular" in Merriam Webster is "of, relating to, or forming a ring". With that, the term annular ring seems redundant to me. A Google search of the phrase returns around 946,000 results, and leads me to question my conclusion.

From what I have found, it appears that annulus would have been a more appropriate choice by the author of this textbook, as that is what the shape in question represents.

Is this usage redundant, or have I missed a subtlety in its usage? For example, does mathematics (especially in calculus and/or geometry) provide for non-annular rings? If so, what distinguishes a ring that is annular from a ring that is not annular but still qualifies as a ring?

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    $\begingroup$ You cannot ask general speakers of English about whether a technical usage in a specialized field is "redundant". $\endgroup$ May 26, 2022 at 18:15
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    $\begingroup$ Redundancy is not a defect. Language is over 90% redundant; it's one of the design features because it allows communication with imperfect transmission, which is the norm. $\endgroup$
    – John Lawler
    May 26, 2022 at 19:29
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    $\begingroup$ @tchrist That argument feels akin to always qualifying "circle" with round: "a car tire is a round circle", to distinguish from phrases such as "a circle of friends". In this case, the context of this being a 'washer' shape tells us what definition of ring should be applied. $\endgroup$
    – Brian
    May 26, 2022 at 19:30
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    $\begingroup$ @Lambie But mathematical rings aren't like physical rings -- they aren't circular, so it's not redundant in that case. $\endgroup$
    – Barmar
    May 26, 2022 at 21:02
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    $\begingroup$ @ryang: I don't know when "line" clearly meant "straight line" began, but I do know that in 1800s literature the word "line" was generally used for planar curves in general (usually algebraic curves, although "usually" here probably because non-algebraic curves were rarely investigated to any great extent). $\endgroup$ May 27, 2022 at 13:15

2 Answers 2


I argue that annular ring is not redundant because in common use annulus and ring are not synonyms. Put another way, not all rings are annular.

The adjective annular is used to emphasize that the ring in question is flat in the sense of being close to planar.

In colloquial use a ring is something tubular (like a donut). That is, a section in a plane crossed by the tube is roughly circular. While annulus has no colloquial use, it generally means something approximating the planar region delimited by two concentric circles. That is, a section in a plane crossed by the tube is roughly a short, wide rectangle. Together an annular ring denominates a sort of flattened tube - that is a washer.

The terminology annular ring is common in electronics where it is used to refer to the ring of copper around a hole drilled through the copper pad on a (generally flat) circuit board.

  • $\begingroup$ The "annular ring" in electronics is the ring of copper left after you drill the hole in the copper pad for the component lead to pass through. $\endgroup$
    – JRE
    May 27, 2022 at 15:13
  • $\begingroup$ @JRE: This is what I was trying to write - I've tried to fix it. $\endgroup$
    – Dan Fox
    May 27, 2022 at 16:03

Perhaps "formally redundant", depending on who you ask. As in the many comments. But/and a certain amount of redundancy can be good, if it saves time and confusion. "Let me repeat that in different words..." :)

In the classes I teach, I do try to explain the sense in which I'll use words, pretending to avoid having to explain at-the-moment, but I do invariably explain at-the-moment also, ... and meta-explain that setting context is surely inescapable for genuine technical communication.

So, yeah, maybe some people would find it redundant, but, manifestly, not everyone. And, apart from the time spent talking about whether it's redundant, it is more efficient to be slightly redundant, to avoid confusion. :)


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