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: hurricanes convert heat energy into mechanical energy. 
Sentence2: Hurricanes use heat to move objects.
Example Output: hurricanes

Example Input: Sentence1: Producers use energy and inorganic molecules to make food. 
Sentence2: Green plants use energy and inorganic molecules to make food.
Example Output: energy

Example Input: Sentence1: lakes are formed by precipitation and runoff. 
Sentence2: The Caspian Sea is, strictly speaking, not really a sea but instead the world's largest lake.
Example Output:
lakes