stupid person; slow-witted person; dimwit
Colloquial and mildly derogatory term for someone who is slow to understand or foolish.
That guy is a dimwit, so no matter how many times you tell him, he doesn't get it.
You can't even do something that simple? What a slow-witted person.
Katakana spelling, sometimes used for emphasis or in informal writing.
Kanji spelling is uncommon; the word is normally written in kana.
The exact derivation is uncertain. It likely combines うすら (a prefix meaning 'slightly' or 'thin') with とんかち (a colloquial term for a blockhead or hammer), yielding a sense of 'a bit of a dimwit'.