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 light bulb is used for seeing in the dark. 
Sentence2: light is required for seeing.
Example Output: seeing

Example Input: Sentence1: Cancer is a disease in which cells divide out of control. 
Sentence2: Cancer is a disease in which cells grow and divide rapidly.
Example Output: Cancer

Example Input: Sentence1: forming coal requires decaying vegetation. 
Sentence2: Bruised or damaged vegetables decay easily.
Example Output:
decaying