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: All oaks are trees. 
Sentence2: Cutting down oaks has a negative impact on an ecosystem.
Example Output: oaks

Example Input: Sentence1: Damage is intensified by moisture stress during drought. 
Sentence2: low amounts of rainfall intensify damage during drought.
Example Output: Damage

Example Input: Sentence1: condensing causes a liquid to form. 
Sentence2: water forms into liquid from the air.
Example Output:
form