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: Lymphocytes are the key cells involved in the immune response. 
Sentence2: The key cells involved in the immune response produce antibodies.
Example Output: cells

Example Input: Sentence1: Weather today is said to be sunny and clear. 
Sentence2: High pressure systems cause it to be sunny.
Example Output: sunny

Example Input: Sentence1: Refrigerators are major users of electricity. 
Sentence2: Keeping food fresh for a long period of time requires a lot of electricity.
Example Output:
electricity