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: Mitosis is cell division. 
Sentence2: mitosis often causes growth.
Example Output: Mitosis

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: the fallopian tubes are used in reproduction. 
Sentence2: the fallopian tubes are used production of offspring.
Example Output:
fallopian