The Collaborative International Dictionary
Lackbrain
Lackbrain \Lack"brain`\, n.
One who is deficient in understanding; a witless person.
--Shak.
Wiktionary
lackbrain
n. (context derogatory English) A person who lacks brains; an idiot.
Usage examples of "lackbrain".
Because he had breached her and drawn a sigh or two from her lips, he now thought her besotted and lackbrained with lust for him.
It had been disappointing not to be able to use it more, but these peasants were such lackbrain weaklings that communication was hardly needed.