Generate an overlapping word between the given two sentences. When you find the overlapping words, they don't have to match exactly, e.g., "survival" and "survive" are valid overlapping words. Little words like "the" or "of" don't count! You must generate significant words which are not the stop words.

Example Input: Sentence1: Basically, heat is energy. 
Sentence2: Head hair is especially important in preventing energy loss from the body.
Example Output: energy

Example Input: Sentence1: Habitat destruction is the primary cause of extinction or threat of extinction for all animals. 
Sentence2: building housing developments may cause extinction.
Example Output: extinction

Example Input: Sentence1: a car engine usually converts gasoline into motion and heat through combustion. 
Sentence2: Gasoline vapors are highly combustible.
Example Output:
gasoline