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: Boiling water can cause burns. 
Sentence2: heating water can cause burns.
Example Output: water

Example Input: Sentence1: Most copepods feed on phytoplankton. 
Sentence2: most copepods feed on bacteria and algae that use sunlight to make food.
Example Output: copepods

Example Input: Sentence1: mineral graphite is used for making pencil lead. 
Sentence2: Mineral graphite and clay are mixed together for a safe alternative to lead.
Example Output:
graphite