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: Energy enters ecosystems in the form of sunlight or chemical compounds. 
Sentence2: Energy enters ecosystems in the form of photons.
Example Output: Energy

Example Input: Sentence1: Combustion-related, motor vehicles, wood burning, open burning, industrial processes. 
Sentence2: Combustion is used to produce heat.
Example Output: Combustion-related

Example Input: Sentence1: zinc has a positive impact on the healing of wounds. 
Sentence2: zinc has a positive impact on animals.
Example Output:
impact