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: if fossils of a water animal or plant are found in a place then that place used to be covered by water in the past. 
Sentence2: Fossils are the remains of prehistoric life.
Example Output: fossils

Example Input: Sentence1: a flower 's purpose is to produce seeds. 
Sentence2: Every job has meaning and purpose.
Example Output: purpose

Example Input: Sentence1: Autumn brings the changing of the seasons. 
Sentence2: Earth 's tilt on its rotating axis causes autumn.
Example Output:
Autumn