In a physical/technical context, I (being not a native speaker) am looking for an adjective that describes the absence of tilt and found “untilted”, which seems however not widely used. More precisely, I want to describe an array of tiltable mirrors in the state where the individual mirrors are not tilted, i.e. lying in the plane of the array.

I feel that “plane” and “flat” are not equivalent synonyms, since they refer to the surface shape, not its orientation. For example, each mirror in that array could be spherically shaped (i.e. not plane/flat), but be untilted at the same time, and vice versa.

“Horizontal” also does not seem applicable, because the overall orientation of the array is not fixed and thus a reference to the horizon/earth makes little sense.

Another idea is to say “all mirrors have zero tilt”, if that is correct English?

Is my understanding of the meaning of these words correct? What might be other precise and comprehensible synonyms for “untilted”?

  • "Orthogonal to the plane of the earth".
    – Hot Licks
    Jan 6, 2016 at 13:52
  • @hot-licks: As I wrote, the orientation w.r.t. earth is arbitrary. Jan 6, 2016 at 13:55
  • 1
    flush (with the surface)?
    – jyc23
    Jan 6, 2016 at 15:38
  • 1
    If the orientation is arbitrary to any possible reference, how can you say it's not tilted??
    – Hot Licks
    Jan 7, 2016 at 2:46
  • @HotLicks The reference is the array I mentioned. E. g. a computer keyboard is an array of buttons and you can say an individual button is pressed independent of the keyboard's orientation (e. g. upside down). Now imagine the buttons to have hinges so that they can tilt instead of doing a piston motion. The keyboard/array itself defines the reference plane I want to implicitly refer to. I want to describe the situation when all buttons (in this picture) are untilted so that their top sides are parallel to the keyboard plane. Maybe I have to add a picture or is it better understandable now? Jan 7, 2016 at 6:55

2 Answers 2


If you are looking for the opposite of tilted when talking about something such as a picture frame or desk, the words upright and and level may suit you.


I'd say that the mirrors are all level.


[lev-uh l]


  1. having no part higher than another; having a flat or even surface.
  2. being in a plane parallel to the plane of the horizon; horizontal.

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