Plural of hairline; the edge of the hair on the forehead and temples, or extremely thin lines.
From Old English 'hær' (hair) + 'line' (from Latin 'linea,' a thread or string) + '-s' (plural). A 'hairline' specifically marks where hair begins.
A receding hairline is one of the most visible signs of aging, which is why hair loss has been a concern for humans for thousands of years—ancient Egyptians even wore wigs and used early hair treatments to combat baldness.
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