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: natural magnetism is used for pointing north by a compass. 
Sentence2: For the ordinary compass, align to the North direction.
Example Output: north

Example Input: Sentence1: Sex hormones are chemical messengers that control sexual development and reproduction. 
Sentence2: Androgens are male sex hormones.
Example Output: Sex

Example Input: Sentence1: transpiration is when water vapor moves from plants into the atmosphere. 
Sentence2: Atmosphere is the blanket of air around the earth.
Example Output:
atmosphere