This idiom describes enduring loyalty, support, or commitment through all circumstances, both good and bad, as if navigating through dense (‘thick’) and sparse (‘thin’) terrain together. It conveys steadfastness or resilience in relationships, partnerships, or endeavors, often used in personal, romantic, or professional contexts to praise unwavering dedication. The phrase carries a tone of admiration, warmth, or solemn promise, reflecting cultural valuing of loyalty and the human capacity for perseverance in adversity. It resonates in stories of enduring bonds or trials, capturing the strength of sticking together, and its rustic imagery adds a layer of timeless simplicity, evoking a journey through varied landscapes. The idiom often celebrates deep trust, making it a heartfelt metaphor for unwavering support or solidarity.

The phrase originated in 14th-century England, rooted in rural imagery of traveling through dense forests (‘thick’) and open fields (‘thin’), symbolizing life’s highs and lows, as noted in Geoffrey Chaucer’s *The Canterbury Tales* (1387): ‘Thorow thikke and thorow thynne.’ The idiom gained traction in the 16th century, reflecting a culture valuing loyalty, as seen in William Shakespeare’s *A Midsummer Night’s Dream* (1595), which explores steadfast love. Its use grew in 19th-century British and American literature, particularly in romantic and heroic narratives, with Charles Dickens’ *David Copperfield* (1850) using it for enduring friendship. The phrase’s adoption was amplified in the 20th century through media, notably in war and family stories like *The New York Times* accounts of soldier camaraderie. Its spread to Commonwealth English came through British influence, and its vivid imagery, evoking a shared journey, and its applicability to loyalty ensured its enduring use across English-speaking cultures, from vows to team spirit.