The Collaborative International Dictionary of English v.0.48:
Sharpen \Sharp"en\, v. t. [imp. & p. p. Sarpened; p. pr. & vb.
n. Sharpening.] [See Sharp, a.]
To make sharp. Specifically:
(a) To give a keen edge or fine point to; to make sharper;
as, to sharpen an ax, or the teeth of a saw.
(b) To render more quick or acute in perception; to make more
ready or ingenious.
The air . . . sharpened his visual ray
To objects distant far. --Milton.
He that wrestles with us strengthens our nerves and
sharpens our skill. --Burke.
(c) To make more eager; as, to sharpen men's desires.
Sharpen with cloyless sauce his appetite. --Shak.
(d) To make more pungent and intense; as, to sharpen a pain
(e) To make biting, sarcastic, or severe. "Sharpen each
word." --E. Smith.
(f) To render more shrill or piercing.
Inclosures not only preserve sound, but increase
and sharpen it. --Bacon.
(g) To make more tart or acid; to make sour; as, the rays of
the sun sharpen vinegar.
(h) (Mus.) To raise, as a sound, by means of a sharp; to
apply a sharp to.