english
1
general::
Phrase(s): *thick as a short plank [and] *thick as two short planks exceptionally dim-witted. (*Also: as ~.) • Dumb? He’s as thick as a short plank, more like. • Oh, I’d not say she was stupid. As thick as two short planks, yes, but stupid? Never!
McGrawhill's American Idioms And Phrasal Verbs