Definition of thicken
1a
: to become dense
the mist thickened
b
: to become concentrated in numbers, mass, or frequency
2
: to grow blurred or obscure
3
: to grow broader or bulkier
4
: to grow complicated or keen
the plot thickens
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Merriam-Webster unabridged
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Time Traveler for thicken
The first known use of thicken was in the 14th century
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