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: a plant requires sunlight to grow. 
Sentence2: Grass needs air and sunlight.
Example Output: sunlight

Example Input: Sentence1: Ribosomes are small organelles where proteins are made. 
Sentence2: Ribosomes are assembled inside the nucleus.
Example Output: Ribosomes

Example Input: Sentence1: lightning can cause a forest fire. 
Sentence2: Static electricity can cause a forest fire.
Example Output:
a