LIGHTEN v. 2 definitions
To burst forth or dart, as lightning; to shine with, or like, lightning; to display a flash or flashes of lightning; to flash. This dreadful night, That thunders, lightens, opens graves, and roars As doth the lion. Shak.
MORSE ALPHABET n.
aper, as, .- (A), -... (B), -.. (D), . (E), .. (O), ... (R), -- (T), etc., or by sounds, flashes of light, etc., with greater or less intervals between them.