A botanical term. noun. A tapering point, as on a leaf or a petal.
"The leaves are conspicuously ovate and concave at base, sheathing the stem, and end in a very long acumen."
--J. -P. Frahm
Sources:
Oxford English Dictionary
J. -P. Frahm, A new contribution to the moss flora of Baltic and Saxon amber, Review of Palaeobotany and Palynology,Volume 129, Issues 1-2, March 2004, Pages 81-101.
<http://www.sciencedirect.com/science/article/B6V6W-4BM8G6F-2/1/11b37c701a30b9e0a737e263cc27fc9f> (June 2, 2008)