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: friction causes an object to lose energy. 
Sentence2: Friction occurs when surfaces rub together.
Example Output: friction

Example Input: Sentence1: plant requires seed dispersal for reproduction. 
Sentence2: plants are pollinated by birds.
Example Output: plant

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