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: Basically the process is pretty simple. 
Sentence2: All cells share some of the same structures and simple processes.
Example Output: process

Example Input: Sentence1: An accounting period is simply a period of time. 
Sentence2: seconds are used to measure a period.
Example Output: period

Example Input: Sentence1: navigation requires knowing direction. 
Sentence2: Direction is designated first in reference to North or South, then to East or West.
Example Output:
direction

