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: the Earth being tilted on its rotating axis causes seasons. 
Sentence2: the planet's orbit and tilt causes seasons.
Example Output: seasons

Example Input: Sentence1: a seismometer is used to measure the strength or magnitude of an earthquake. 
Sentence2: Seismometer Calibration : Instructions on how to calibrate a homemade seismometer.
Example Output: seismometer

Example Input: Sentence1: coal is used to produce electricity by burning in coal-fire power stations. 
Sentence2: coal is used to produce energy by burning in coal-fire power stations.
Example Output:
burning