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: Weather today is said to be sunny and clear. 
Sentence2: High pressure systems cause it to be sunny.
Example Output: sunny

Example Input: Sentence1: adding salt to a solid decreases the freezing point of that solid. 
Sentence2: Water density decreases with temperature and increases with salt content.
Example Output: decreases

Example Input: Sentence1: Muscle contraction occurs when muscle fibers get shorter. 
Sentence2: Muscles can only contract and relax.
Example Output:
contraction