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: cell division often causes growth. 
Sentence2: Mitosis is cell division.
Example Output: cell

Example Input: Sentence1: Hydrogen bonds cause water to expand when it freezes. 
Sentence2: Water freezes into ice when cooled.
Example Output: freezes

Example Input: Sentence1: powering an electrical device with a battery requires a path for electricity to flow through a closed circuit. 
Sentence2: A battery-powered computer requires a closed circuit for electricity to flow.
Example Output:
battery