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Webster 1913 Edition

Adj.

Needle-shaped; slender like a needle or bristle, as some leaves or crystals; also, having sharp points like needles.

A-cic′u-lar-ly

adv.

Adj.

[L. acicula, Priscian, a needle, from Gr., L. a point. See Acid.]

In the shape of a needle; having sharp points like needles.

An acicular prism is when the crystals are slender and straight.