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 solution is formed by one substance being dissolved in another substance. 
Sentence2: A solution is formed when limestone is dissolved in ocean water.
Example Output: formed

Example Input: Sentence1: Antibiotics and vaccines are being stockpiled as Britain gears up to meet the bioterrorism threat. 
Sentence2: Antibiotics and vaccines are being stockpiled against another potential threat in the environment.
Example Output: Antibiotics

Example Input: Sentence1: Bile , synthesized by the liver, contains HCO3-, bile salts and bile pigments. 
Sentence2: The liver reduces the acidity of food entering from the highly acidic stomach.
Example Output:
liver