MEANING: noun: A careless error in thinking.

ETYMOLOGY: From think, formed on the pattern of typo (typographical error). Earliest documented use: 1990s.

NOTES: When someone makes a typo and spells “teh” instead of “the”, it’s not that they don’t know the spelling of the word “the”. A thinko works the same way: it’s a glitch in one’s thinking, perhaps due to a distraction, tiredness, etc.

THINKA - famous Rodin sculpture on loan to Boston's Museum of Fine Arts

THICKO - antisocial psychopath with a list

THINNO - opposite of a thicko