Generate a topic word for the given sentence. A topic word is usually the name of a person, place, animal, concept or object the sentence is focusing on.

Example Input: in organic chemistry, an epoxide is a molecule that has a ring with at least three atoms in total, two carbon atoms and one oxygen atom.
Example Output: epoxide

Example Input: the cyclostomes (or cyclostomata) are the lamprey and hagfish.
Example Output: cyclostome

Example Input: tamahagane {tah-mah-ha-ga-nay} is a high quality metal (steel) made in the japanese tradition.
Example Output:
tamahagane