thick as two planks


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thick as two planks

or

thick as two short planks

BRITISH, INFORMAL
If someone is as thick as two planks or as thick as two short planks, they are very stupid. His people regarded him as a great and wise king. In fact he was as thick as two planks.
See also: plank, thick, two

thick as two (short) planks

very stupid. informal
Variants of this expression include thick as a plank and thick as a brick . There is a play on thick in its basic sense ‘of relatively great depth from side to side’ and its colloquial sense ‘stupid’.
See also: plank, thick, two