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: wind is used for producing electricity. 
Sentence2: Winds are caused by pressure differences.
Example Output: wind

Example Input: Sentence1: Cells are the units of function in living things. 
Sentence2: living things cannot survive without oxygen.
Example Output: living

Example Input: Sentence1: Rivers are usually larger than streams. 
Sentence2: Rivers are larger than the bodies of water they're divided into.
Example Output:
Rivers