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: Cancer is a disease in which cells divide out of control. 
Sentence2: Cancer is a disease in which cells grow and divide rapidly.
Example Output: Cancer

Example Input: Sentence1: looking at bright objects has a negative impact on the eyes. 
Sentence2: Looking at bright objects have a negative impact on the retina.
Example Output: bright

Example Input: Sentence1: Also pyrite within the altered wall rock is oxidized to limonite, geothite and hematite. 
Sentence2: chemical weathering causes pyrite to change to limonite, geothite and hematite.
Example Output:
geothite

