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: Interstellar space contains a plasma. 
Sentence2: interstellar space contains electrons, atoms, and stars.
Example Output: Interstellar

Example Input: Sentence1: cell division often causes growth. 
Sentence2: Cell division leads to reproduction.
Example Output: cell

Example Input: Sentence1: Stems Stems are the support structures of a plant. 
Sentence2: Support structures of a plant are sometimes used to store water.
Example Output:
structures