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: Some mollusks are nearly microscopic. 
Sentence2: Some squids are nearly microscopic.
Example Output: Some

Example Input: Sentence1: Roundworms make up the phylum Nematoda. 
Sentence2: Also, nematoda and rotifera are important groups contributing to soils.
Example Output: Nematoda

Example Input: Sentence1: gravity pulls objects towards planets. 
Sentence2: Gravity pulls objects around the sun.
Example Output:
gravity