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: electric devices require electrical energy to function. 
Sentence2: Lie detectors are electrical or mechanical devices.
Example Output: devices

Example Input: Sentence1: Some pelycosaurs gave rise to a group of animals called therapsids. 
Sentence2: Like most other groups of synapsids, all pelycosaurs are now extinct.
Example Output: pelycosaurs

Example Input: Sentence1: a sifter is used for separating mixtures. 
Sentence2: a sifter is used for some recipes.
Example Output:
sifter