Brontophobia: An abnormal and persistent fear of thunder that causes undue anxiety even though sufferers realize that thunder itself poses no threat to them. When outdoors during a thunderstorm, they may suffer excessive anxiety. When indoors, they may hide under beds or desks, behind sofas, or in closets.
"Brontophobia" is derived from the Greek "bronte" (thunder) and "phobos" (fear). This same Greek word has given us the English word "brontometer," an instrument for recording the activity of thunderstorms.
A related term: Astraphobia, fear of thunderstorms.