Abstract
The paper deals with the etymology of exclusive Czech words pošetilý 'foolish, inept' and older pošetiti se 'to go mad, to take leave of one's senses'. The words are not attested in Old Czech, but they emerge in high numbers in the Middle Czech period.
The explanations in Czech etymological dictionaries to this point do not offer any convincing solution. The present paper proposes that pošetiti se is derived from Old Czech šiet '(very) old man', and suggests a semantic development 'to behave like an old man' RIGHTWARDS ARROW 'to become foolish'.