The highway department is currently enlarging a tunnel, not to widen it but to... what? Is there a single verb that means to increase the vertical dimension of something? (For purposes of this question it does not matter whether they're doing that by modifying the floor or the ceiling.)

Raise is not correct because raising doesn't change size, only elevation. One can talk about raising the ceiling (which is how they are enlarging the tunnel), but that's not a single word. Heighten (suggested in an answer) seems questionable, e.g. from thefreedictionary.com "to make high or higher; raise".

If I were looking for an adjective this wouldn't be a problem; "tall" would suit. But it doesn't have a corresponding verbal form, and dictionary entries aren't giving me hints.

  • For one, actually two, your title is misleading. 'Height' brings up an image of distance above ground level. Plus, this here is not a structure but the absence of one, a hollow. [editing ...]
    – Kris
    Apr 19 '12 at 16:27
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    I like "embiggen"....
    – Hellion
    Apr 19 '12 at 16:45
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    @Hellion, I do too, but it's not specific about the direction of embiggening. Apr 19 '12 at 16:46
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    If you're really talking about a tunnel, I think heighten is fine. Most people, upon hearing "the tunnel is being heightened", will think its vertical clearance is being increased. Further, most will think this is being achieved by raising its roof (rather than by lowering its floor). If you specifically want a word that equally applies to lowering the floor, or to an abstract, general case beyond tunnels, then yeah, it will be tough to find a single-word answer.
    – John Y
    Apr 19 '12 at 22:14
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    Regarding a strict, dictionary interpretation of heighten: Natural language is not orthogonal. One of the definitions of height is "vertical extent", i.e. tallness. Someone who is six feet tall has a height of six feet. A high stool refers to a stool with long legs resting on the floor, not to a short stool resting on a raised platform. So relax about heighten. It encompasses "entallening".
    – John Y
    Apr 19 '12 at 22:27


v. to increase the height of; make higher.

From the Farlex Free Dictionary

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    This seems like "raise" and the definition isn't clear on that point. Have you heard it used this way (not applied to a ceiling but to a space)? Apr 19 '12 at 15:46
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    @MonicaCellio: If someone said "The highway department is currently enlarging a tunnel, to heighten it" I would understand that to mean that the distance between floor and ceiling would be greater than before, once they finished the job. Apr 19 '12 at 15:52
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    @FrustratedWithFormsDesigner, in conjunction with "enlarge" I agree. Would it be clear if someone just said "the highway department is currently heightening the tunnel"? (I've heard people say "...widening the tunnel" and that's perfectly understandable.) Apr 19 '12 at 15:57
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    If they're digging the floor, you would say they're "deepening" the tunnel. Although, out of context that would imply tunneling deeper into something, like the side of a mountain.
    – Taj Moore
    Apr 19 '12 at 20:34
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    +1 for immediate understanding, this was my first thought on reading the question.
    – user14070
    Apr 19 '12 at 20:53

I couldn't come up with one word, and I know you said in your question that raise is not the right word, but it looks like when engineers enlarge a tunnel by making it taller they say they are going to raise the roof. They also use the phrase increased clearance for a tunnel that is made taller.

(And I know you didn't ask this, but it also appears that tunnel roof is preferred to tunnel ceiling.)

See this link for use of "raise the roof" in more technical documents.

See this link for NGram of tunnel ceiling vs. tunnel roof.

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    While this sort of question is often an interesting thought experiment, most of the time I'm left thinking “why is a single word required?” I would just say they are increasing the clearance of the tunnel.
    – ghoppe
    Apr 19 '12 at 17:46
  • @ghoppe, it was just for what felt like better flow -- they're finally ____ing the tunnel so maybe trucks will stop wedging themselves in it. Apr 19 '12 at 23:25
  • JLG, thanks for the links -- didn't know about ceiling vs. roof in that case. Apr 19 '12 at 23:26
  • @MonicaCellio In that case, what's wrong with enlarging? I mean, it's pretty obvious from that context and physical dimensions of trucks and tunnels that the trucks won't get wedged in by the sides. ;)
    – ghoppe
    Apr 19 '12 at 23:28

The only option seems to be to expand vertically, unless there's a surprise candidate!


The verb I would use, at least with regard to a tunnel, is deepen.

The highway department seems to want to dig deeper into the ground to provide more space for the tunnel. "Raising" it (aboveground), doesn't make much sense, because they have all the space in the world above ground.

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