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: Diurnal cycles Diurnal cycles are the daily cycles of light and darkness. 
Sentence2: Plants detect and respond to diurnal cycles.
Example Output: Diurnal

Example Input: Sentence1: cell division often causes growth. 
Sentence2: Mitosis is cell division.
Example Output: cell

Example Input: Sentence1: Through weathering, the surface was eroded away, exposing igneous rock. 
Sentence2: Eroding means breaking down rocks from larger whole into smaller pieces of rocks.
Example Output:
eroded