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: Any antigen that causes an allergy is called an allergen. 
Sentence2: Antigens are proteins foreign to the body.
Example Output: antigen

Example Input: Sentence1: Many plants respond to the days growing shorter in the fall by going dormant. 
Sentence2: Many plants respond to the autumnal equinox by going dormant.
Example Output: Many

Example Input: Sentence1: a telephone is used for communication by humans over long distances. 
Sentence2: Communication is about the sharing of ideas, thoughts and points of views.
Example Output:
communication