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: Trees have woody stems covered with bark. 
Sentence2: Evergreens have woody stems covered with bark.
Example Output: bark

Example Input: Sentence1: Climate refers to weather over a long period of time. 
Sentence2: weather is generally described in terms of temperature and moisture.
Example Output: long

Example Input: Sentence1: Mutualism is a symbiotic relationship in which both species benefit. 
Sentence2: Mutualism is a relationship like that of microbes and mussels in which both species benefit.
Example Output:
Mutualism