Brain wave and Blue sky

Brain wave noun - (neurophysiology) rapid fluctuations of voltage between parts of the cerebral cortex that are detectable with an electroencephalograph.

Blue sky and brain wave are semantically related In some cases you can use "Blue sky" instead an adjective phrase "Brain wave".

Blue sky noun - The sky as viewed during daylight.

Brain wave and blue sky are semantically related in creative topic. Sometimes you can use "Brain wave" instead an adjective phrase "Blue sky".