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: a flashlight requires a source of electricity to produce light. 
Sentence2: Flashlights provide the safest emergency lighting source.
Example Output: flashlight

Example Input: Sentence1: Climate Forests stabilize climate. 
Sentence2: forests stabilize what is generally described in terms of temperature and moisture.
Example Output: Forests

Example Input: Sentence1: Prokaryotes are single-celled organisms that lack a nucleus. 
Sentence2: An organism is a living thing.
Example Output:
organisms