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: Fertilization occurs naturally in the fallopian tubes. 
Sentence2: fertilization is used for reproduction.
Example Output: Fertilization

Example Input: Sentence1: Autumn brings the changing of the seasons. 
Sentence2: Earth 's tilt on its rotating axis causes autumn.
Example Output: Autumn

Example Input: Sentence1: a tape measure is used to measure length. 
Sentence2: A tape measure is used to see how long something is.
Example Output:
measure