A lock of hair that falls across the forehead; also, a pin or wedge used to secure something in place.
From 'fore-' (front) + 'lock' (hair or mechanism). The meaning split in English: one sense refers to hair on the forehead, while the other derives from mechanical 'lock' meaning a fastening device.
When sailors grabbed 'the forelock' in the phrase 'taking time by the forelock,' they were literally grabbing the hair hanging forward—personifying Time as something you had to physically grab or it would escape.
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