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 converts chemical energy into light energy. 
Sentence2: Only as long as there are batteries in the flashlight, the flashlight will function.
Example Output: flashlight

Example Input: Sentence1: All cells share some of the same structures and basic functions. 
Sentence2: Inside the cell is a structure called the nucleus.
Example Output: cells

Example Input: Sentence1: Another named half of the earth is the so-called Pacific hemisphere. 
Sentence2: when half of Earth is tilted towards the sun , that half of Earth receives more direct sunlight.
Example Output:
earth