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: Lions live in social groups called prides. 
Sentence2: Chimpanzees live in social groups called communities.
Example Output: groups

Example Input: Sentence1: Pedigree A pedigree is a map of the types of hemoglobin in the family tree. 
Sentence2: a map of the types of hemoglobin in the family tree is a useful tool for studying inheritance patterns.
Example Output: family

Example Input: Sentence1: microorganisms can cause infections. 
Sentence2: microorganisms can cause diseases.
Example Output:
microorganisms