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: Dinosaur bones, like many other artifacts, are fossilized. 
Sentence2: radioactive dating is used to determine the age of dinosaur bones.
Example Output: Dinosaur

Example Input: Sentence1: Bryophytes occupy niches in moist habitats. 
Sentence2: Animals and plants that live in the same place and share resources form a community biome niche .
Example Output: niches

Example Input: Sentence1: After a sperm and egg unite, they form an embryo. 
Sentence2: fertilization occurs with the formation of the embryo.
Example Output:
embryo