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: Many birds perform elaborate courtship dances. 
Sentence2: Many birds perform dances before they mate.
Example Output: Many

Example Input: Sentence1: waxy leaves are used for storing water by some plants. 
Sentence2: waxy leaves are used for water conservation by some plants.
Example Output: leaves

Example Input: Sentence1: Growth is faster during infancy than it is during puberty. 
Sentence2: Growth is faster in infancy than in adolescence.
Example Output:
Growth