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: Echinoderms lack respiratory and excretory systems. 
Sentence2: echinoids lack a respiratory system.
Example Output: respiratory

Example Input: Sentence1: when a gas in an open container evaporates , that gas spreads out into the air. 
Sentence2: when a gas in an open container evaporates gas molecules slamming into one another.
Example Output: container

Example Input: Sentence1: Viruses are usually considered to be nonliving. 
Sentence2: The things that are the smallest agents of disease are usually considered to be nonliving.
Example Output:
considered