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: Many corals secrete an exoskeleton that builds up to become a coral reef. 
Sentence2: Good examples are Bubble coral, Elegance coral, Frogspawn and other Euphyllia corals.
Example Output: coral

Example Input: Sentence1: a camera is used for recording images. 
Sentence2: a camera is used for recording binary.
Example Output: camera

Example Input: Sentence1: Output of the fan is varied by means of a series of adjustable vanes upstream of the impeller. 
Sentence2: fan speed is adjustable.
Example Output:
adjustable

