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: Basically the process is pretty simple. 
Sentence2: All cells share some of the same structures and simple processes.
Example Output: process

Example Input: Sentence1: Plants use unsaturated fatty acids to store energy. 
Sentence2: Plants and fish contain fatty acids.
Example Output: Plants

Example Input: Sentence1: Carbon is the fuel source. 
Sentence2: A fuel source may be stored in sedimentary rock for millions of years.
Example Output:
fuel