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: the vickers machine gun (also known as the vickers gun) was a machine gun that was used by the british army from 1912 to 1968.
Example Output: vickers machine gun

Example Input: monosemy is when the words in a language each have only one meaning.
Example Output: monosemy

Example Input: northern rhodesia was a territory in south central africa.
Example Output:
northern rhodesia