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.

Sentence1: Dams are very damaging to rivers. 
Sentence2: Creating a lake can be very damaging to rivers.
damaging

Sentence1: the moon revolving around the Earth causes the phases of the moon. 
Sentence2: Lets start our discussion of the Moon's phases with the New Moon phase.
phases

Sentence1: a switch is used to start the flow of current in an electrical circuit. 
Sentence2: Electric power is ready to use at the flip of a switch.

switch