Abbrev. for Canadian National railway, Canada's largest railway company. This company has a history dating back to 1836, which can be traced through the acquisition and liquidation of 200 seperate rail companies.

They also built the CN Tower (the "World's Tallest Building and Free Standing Structure"), in 1976 as a display of Canada's industrial prowress.
Also the CYANO radical (charge -1):
Used in pharmaceuticals, steroids and other basic compounds.
Also the country code for China (.cn)

Also "Cranial Nerve" in CN Examination.
A Cranial Nerve Examination I is a simple olfactory test where the sense of smell in the patient's nostrils are tested seperately. Intended to detect traumatic disruption of olfactory nerves.
A CN Exam II is an optic test where the ability of each of the patient's eyes to focus. This test will detect eye problems due to intracranial pressure, or optic atrophy from optic nerve lesions.
nodeshell challenge from m1a9366b. He did a kickin' writeup for a Times of Lore nodeshell I threw his way.