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: a stopwatch is used to measure time. 
Sentence2: Time can be measured with a clock or watch.
Example Output: measure

Example Input: Sentence1: Thrinaxodon, a small Lystrosaurus Zone cynodont, shows many of the characters of the group. 
Sentence2: Thrinaxodon is from the animal family that eventually evolved into mammals.
Example Output: Thrinaxodon

Example Input: Sentence1: Flatworms belong to the phylum Platyhelminthes. 
Sentence2: Flatworms belong to the free-living and parasitic forms.
Example Output:
Flatworms