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: Cnidarians have a hydrostatic skeleton. 
Sentence2: Jellyfish have a hydrostatic skeleton.
Example Output: hydrostatic

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

Example Input: Sentence1: damming a river can cause a lake to form. 
Sentence2: Creating a lake can be very damaging to rivers.
Example Output:
a