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: Bees feed on nectar and pollen. 
Sentence2: Plant reproduction often requires bees and nectar.
Example Output: Bees

Example Input: Sentence1: Organic matter is the byproduct of the decomposition. 
Sentence2: organic matter is increased by decomposing.
Example Output:
decomposition