In civil engineering, the words invert and obvert are used in the context of pipe elevations. I gather that invert means: interior bottom elevation of pipe, and obvert means: interior top elevation of pipe.

This is a diagram of a pipe with arrows labeling the various parts. The crown is the outer top, the obvert is the inner top, and the invert is the inner-bottom. It also illustrates the external and internal diameters, with Size = Nominal internal Diameter(DD) near the upper right corner, with an arrow pointing to the inner diameter

However, using the word invert in this context seems strange to me. To me, none of these definitions fit:

Invert (Merriam-Webster)

  1. a: to reverse in position, order, or relationship
    b: to subject to inversion
  2. a: to turn inside out or upside down
    b: to turn inward
  3. a: to find the mathematical reciprocal of
    b: to divide using fractions, invert the divisor and multiply

What does the word invert have to do with pipes? What has been inverted?

  • Ultimately, it's jargon.
    – Hot Licks
    Commented Apr 7, 2017 at 21:45
  • 1
    Nothing wrong with jargon: we even have a tag for it. By all means edit it in if that tag is appropriate here. I'm not sure it is (but then I trained as an engineer, so whether it's jargon or not may be difficult to determine).
    – Andrew Leach
    Commented Apr 7, 2017 at 22:31
  • @AndrewLeach I just tried, but it didn't take effect. It appears to already be categorized as a tag synonym of terminology, which the question already had.
    – Tonepoet
    Commented Apr 7, 2017 at 23:12
  • 1
    This online dictionary actually has the best explanation: dictionary.com/browse/ob- [...]but now used also, with the sense of “reversely,” “inversely,” to form Neo-Latin and English scientific terms: object; obligate; oblanceolate. If you take invert and obvert together, the obvert is the reverse of the invert.
    – Lambie
    Commented Apr 8, 2017 at 16:36
  • The inverted arch thing would make even more sense to me if, historically, pipes were just trenches/inverted arches/channels, and not tubular.
    – User1974
    Commented Apr 8, 2017 at 16:38

2 Answers 2


The Century Dictionary and Cyclopedia s.v. Invert: In architecture, an inverted arch; specifically, the floor of the lock-chamber of a canal, which is usually in the form of an inverted arch, or the bottom of a sewer.

The bottom of the sewer is called the invert from a general resemblance in construction to an "inverted" arch. Mayhew, London Labour and London Poor, II 445.

A list of dictionary definitions from the Century Dictionary and Cyclopedia, with the quoted entry in a red box.


See the noun part of invert at Oxford dictionary

An arch constructed in an upside-down position to provide lateral support, e.g. in a tunnel.


So you see, the bottom concave part is like an upside down arch, which is in discussion here.

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