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: Genetics is the study of inheritance. 
Sentence2: Pedigrees are useful tools for studying genetics.
Example Output: Genetics

Example Input: Sentence1: Basically, heat is energy. 
Sentence2: Head hair is especially important in preventing energy loss from the body.
Example Output: energy

Example Input: Sentence1: Feathers help birds fly and provide insulation. 
Sentence2: Penguins rely on their feathers for insulation.
Example Output:
insulation