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: Plants exhibit phototropism, or growing toward a light source. 
Sentence2: Phototropism means growing toward the energy of light.
Example Output: phototropism

Example Input: Sentence1: Mollusks are invertebrates such as the common snail. 
Sentence2: snails have no backbone.
Example Output: snail

Example Input: Sentence1: erosion causes deposition. 
Sentence2: Silica sand is primarily mined from sandstone deposits.
Example Output:
deposition