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: wind is used for producing electricity. 
Sentence2: Winds are caused by pressure differences.
Example Output: wind

Example Input: Sentence1: creating paper requires cutting down trees. 
Sentence2: Trees begin as epiphytes on host trees.
Example Output: trees

Example Input: Sentence1: condensing means changing from a gas into a liquid by reducing heat energy. 
Sentence2: condensing means the opposite change of state to boiling.
Example Output:
condensing