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: Amphibians are the first true tetrapods, or vertebrates with four limbs. 
Sentence2: Frogs are classified as amphibians.
Example Output: Amphibians

Example Input: Sentence1: if an object is made of a material then that object has the properties of that material. 
Sentence2: items properties are the same as the materials the item is made of.
Example Output: made

Example Input: Sentence1: Gases as well as vapours can contaminate the workplace air. 
Sentence2: When dangerous gas from an open container evaporates, it can contaminate a workplace.
Example Output:
contaminate