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The Collaborative International Dictionary of English v.0.48 (gcide)

Compasses \Com"pass*es\, n., pl.
An instrument for describing circles, measuring figures,
etc., consisting of two, or (rarely) more, pointed branches,
or legs, usually joined at the top by a rivet on which they
move.
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Note: The compasses for drawing circles have adjustable pen
points, pencil points, etc.; those used for measuring
without adjustable points are generally called
dividers. See {Dividers}.
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{Bow compasses}. See {Bow-compass}.

{Caliber compasses}, {Caliper compasses}. See {Calipers}.

{Proportional}, {Triangular}, etc., {compasses}. See under
{Proportional}, etc.
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Triangular \Tri*an"gu*lar\, a. [L. triangularis: cf. F.
triangulaire.]
1. Having three angles; having the form of a triangle.
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2. (Bot.) Oblong or elongated, and having three lateral
angles; as, a triangular seed, leaf, or stem.
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{Triangular compasses}, compasses with three legs for taking
off the angular points of a triangle, or any three points
at the same time.

{Triangular crab} (Zool.), any maioid crab; -- so called
because the carapace is usually triangular.

{Triangular numbers} (Math.), the series of numbers formed by
the successive sums of the terms of an arithmetical
progression, of which the first term and the common
difference are 1. See {Figurate numbers}, under
{Figurate}.
[1913 Webster]