This phrase is often a metaphor indicating extreme wealth or comfort, not necessarily a physical 'lap'. With his new promotion, James was in the lap of luxury, financial worries a thing of the past.
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Cultural Depiction
It may be used to describe the opulent lifestyles seen in films or literature. The novel depicts the aristocracy as sitting in the lap of luxury, untouched by common struggles.
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Irony or Sarcasm
Sometimes used ironically to emphasize poverty or lack of comfort. Living in a cramped, leaky apartment, he joked about being in the lap of luxury.