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: Adaptation traits contribute to individual fitness and to the evolution of animal genetic resources. 
Sentence2: Behaviors can improve the evolution of animal genetic resources.
Example Output: animal

Example Input: Sentence1: All life relies on a relatively narrow range of pH, or acidity. 
Sentence2: humans rely on a relatively narrow range of acidity.
Example Output: acidity

Example Input: Sentence1: the looseness of soil has a positive impact on a plant 's roots' growth in that soil. 
Sentence2: Pinions tolerate drought and alkaline soil, but prefer loose, well-drained soils.
Example Output:
looseness