Mer makeup

As a detective trying to solve the mystery of the crossword clue ‘Mer makeup’, I first deduced that “Mer” likely referred to the French word for “sea” (mer). From there, I considered possible makeups or components of the sea. One such component could be “water”, but that was too short to fit in the crossword puzzle. Another option was “salt”, but again, too short. That’s when another thought struck. Sea water, or any water for that matter, needs a particular chemical compound to make it safe for consumption: EAU. Eau is the French word for water, and it fits perfectly within the crossword puzzle. Mystery solved!