acicula

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A slender, needlelike part or structure, such as a spine or bristle of certain plants and animals or a crystal of certain minerals.

from The Century Dictionary.

• noun A needle, pin, or bodkin, of wood or bone, used by Roman women as a hair-pin. It was not smaller than an acus (which see), but of inferior material.
• noun A spine or prickle of an animal or plant. Also called acicle.
• noun A name applied to several genera of gastropods, and retained for the representative genus of the family Aciculidæ, inhabiting Europe. A. fusca is the best-known form.
• noun A genus of worms.
• noun Plural of aciculum.
• noun In botany: The bristle-like prolongation of the rachilla of a grass-spike.
• noun A tooth-like process in the hymenium of certain fungi.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Nat. Hist.) One of the needlelike or bristlelike spines or prickles of some animals and plants; also, a needlelike crystal.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun One of the needlelike or bristlelike spines or prickles of some animals and plants; also, a needlelike crystal.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a needlelike part or structure of a plant or animal or crystal; as a spine or bristle or crystal