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: If there is an increase in UV radiation, the risks go up for all types of skin cancer. 
Sentence2: Ozone depletion increases the risks for all types of skin cancer.
Example Output: all

Example Input: Sentence1: Results can be damaging or disastrous. 
Sentence2: Lack of immunization can be damaging or disastrous.
Example Output: damaging

Example Input: Sentence1: Vertebrate chordates have a backbone. 
Sentence2: Invertebrates are animals who lack a backbone or spinal column.
Example Output:
backbone