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: wind is used for producing electricity. 
Sentence2: Wind is caused because of pressure differences in the atmosphere.
Example Output: wind

Example Input: Sentence1: Stress is the applied force, strain is the change in shape. 
Sentence2: Paper is crumbled when stress and strain is applied in order to change the shape.
Example Output: Stress

Example Input: Sentence1: clouds are formed by water vapor rising into colder regions of the atmosphere and condensing. 
Sentence2: clouds are formed by h2o vapor rising into colder regions of the atmosphere and condensing.
Example Output:
atmosphere