What's the meaning of the phrase 'Absent-minded professor'?
An absent-minded professor is someone (usually male) who is habitually inattentive or forgetful and distracted to the extent of being unaware of his immediate surroundings.
The allusion is to a bumbling academic who is so preoccupied with abstract thought as to forget to engage with the real world. The image presented is usually of someone who neglects their appearance and fails to be aware of other people and events.
What's the origin of the phrase 'Absent-minded professor'?
The archetype of the absent-minded professor actually wasn't a professor at all but a Greek philosopher. Plato recorded an incident involving the philosopher Thales in Theaetetus, circa 369BC. The story (and it probably is just a story) is that Thales absent-mindedly fell into a pit while walking along gazing at the stars.
The great English scientist and bone-fide genius Sir Isaac Newton also had a reputation of being so engrossed in his work as to forget the niceties of life, even to the point of forgetting to eat for days at a time. The obsessiveness of Newton's approach to his work, and other recorded behaviour, suggests that he had Asperger's Syndrome. While post-mortem diagnosis is a dangerous game, Newton's behaviour throughout his life fits strongly with the known symptoms of Asperger's. Perhaps 'Asperger's-minded' would be a reasonable alternative name for this type of absent-minded behaviour.
More recently, Albert Einstein has become the poster boy for the absent-minded professor type. This is probably more to do with his unruly hairstyle than anything about his personality, which was anything but unworldly.
Despite having examples of 'absent-minded professor' types over the millennia the term itself is quite modern.
There is a reference to an absent-minded professor in a medical textbook published by Freeman Bumstead in 1859 but this appears to be a literal reference to a professor who had forgotten something rather than the meaning we now give to the phrase.
The first use that I know of 'absent-minded professor' being used in the way we now use it is from a feeble joke published in the US newspaper the Argus and Patriot, October 1861:
An absent minded professor, in going out of the gateway of his college, ran against a cow; in the confusion of the moment he raised his hat and exclaimed: "I beg your pardon, madame." Soon after he stumbled against a lady in the street; in sudden recollecting his former mishap, he called out: "Is that you again you brute?"
The joke may be less than hilarious but it was reprinted in numerous American newspapers in 1861 and it seems highly likely that a new phrase in the language was coined there and then.