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: an animal requires air for survival. 
Sentence2: The Moon has no atmosphere and no air.
Example Output: air

Example Input: Sentence1: After a seed is planted it is watered. 
Sentence2: seeds need water.
Example Output: seed

Example Input: Sentence1: measuring the hardness of minerals requires scratching those materials. 
Sentence2: Classifying minerals requires scratching those materials.
Example Output:
materials