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: Humans have collected and grown mushrooms for food for thousands of years. 
Sentence2: Yeast and mushrooms are types of fungus.
Example Output: mushrooms

Example Input: Sentence1: moss causes chemical weathering. 
Sentence2: If the moss was completely dried then it is dead.
Example Output: moss

Example Input: Sentence1: fire converts chemical energy into light and heat energy. 
Sentence2: Fires ignited with fuel convert energy into light and heat.
Example Output:
converts