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: Coral reefs are made up of the accumulated exoskeletons of the coral polyp. 
Sentence2: coral polyps form reefs.
Example Output: polyp

Example Input: Sentence1: riding a bike does not cause pollution. 
Sentence2: riding a bike does not release particles.
Example Output: bike

Example Input: Sentence1: wind causes erosion. 
Sentence2: Erosion affects farm viability.
Example Output:
erosion