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: a fire requires oxygen to burn. 
Sentence2: If the oxygen is removed, the fire is smothered.
Example Output: oxygen

Example Input: Sentence1: Endospores are commonly found in soil and water. 
Sentence2: Dirt is really misplaced soil.
Example Output: soil

Example Input: Sentence1: disease has a negative impact on an organism. 
Sentence2: Because it is a disease, it can be treated.
Example Output:
disease