Longman Dictionary of Contemporary English
Wiktionary
n. 1 The hollow part of the root of a tooth containing the nerve and blood vessels. 2 (context dentistry English) A surgical operation on a root canal, typically filling it with gutta-percha.
WordNet
n. the passage in the root of a tooth through which its nerve and blood vessels enter the pulp cavity
Wikipedia
A root canal is the anatomic space within the root of a tooth. Part of a naturally occurring space within a tooth, it consists of the pulp chamber (within the coronal part of the tooth), the main canal(s), and more intricate anatomical branches that may connect the root canals to each other or to the surface of the root.
Usage examples of "root canal".
How many times did she hear yet one more tale about someone's fillings falling out or a root canal going bad or a crown that looked like a piano key cracking smack in half for no good reason?
My mouth felt better, but in another two weeks I had a third root canal, in the upper right jaw, to clear up the smaller remaining sensitivity.
In the root canal of the claw we found some matter, which is now being sequenced for DNA.