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: Combustion generates toxic fumes. 
Sentence2: High temperatures can cause toxic fumes.
Example Output: fumes

Example Input: Sentence1: Some birds are pollinators that co-evolved with plants. 
Sentence2: insects pollinate plants.
Example Output: plants

Example Input: Sentence1: Aging occurs as cells lose their ability to divide. 
Sentence2: aging occurs as mitosis stops.
Example Output:
Aging