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: All monkeys are mammals. 
Sentence2: monkeys conserve body heat with their hair or fur.
Example Output: monkeys

Example Input: Sentence1: Interest in fossils is worldwide. 
Sentence2: paleontologists study something with worldwide interest.
Example Output: Interest

Example Input: Sentence1: An ecosystem is like a neighborhood in nature. 
Sentence2: A wildfire changes a neighborhood in nature drastically.
Example Output:
nature