Etymology is a great field for the amateur sleuth. Can’t you just picture a word nerd donning a deerstalker cap and piloting a big magnifier to ferret out early citations for a word? You know, there are some people who put quite a lot of time and energy into antedating words – finding citations that show that the word was in use earlier than previously thought, and perhaps giving some clue as to where it came from. One might imagine it as being like a bloodhound, sniffing the old foxed library books for the faint hints of a lexical trail.
Those of us who benefit from the lucubrations of such dedicated geeks can be more slothful. If I want to sleuth out the origin of a word, all I need do is consult a good etymological dictionary, as long as it has the info. If I want to know what words it is used with, there are corpus databases for that. And if I want to know what other words could be influencing it by resemblance… well, no one is doing formal studies on that, so the best I can do is taste, imagine, surmise.
What does sleuth mean to you? Yes, ‘detective’, certainly, as in the common collocation amateur sleuth; it is also a verb, as in sleuth it out. But what image do you get? Popular culture has some images it has determined, thanks to books and movies. But can you use the term for any detective? Is Mike Hammer a sleuth? Sam Spade? Hercule Poirot? Miss Marple? Jessica Fletcher? Sherlock Holmes? Are they all equally sleuthy, or do you tend more to have an image of, say, the Basil Rathbone version of Sherlock Holmes, with the deerstalker cap (as opposed to the Jeremy Brett version, top-hatted and more accurate to the books and also very entertaining, or the more recent Holmses such as Robert Downey Jr. or Benedict Cumberbatch)? Is a tough-guy detective not soft and subtle enough to be a sleuth slinking like soft silk through the dark alleys and drawing rooms?
If so, is this just an effect of which image is strongest- and longest-established, or does it have something to do with the sound of the word, coming and going with voiceless fricatives and, between them, the liquid /l/ and that dark, hollow high back vowel /u/? It slips and slides but sounds as though it seeks the truth like a soothsayer. Try this for comparison: in German, the word for ‘key’ is Schlüssel. Which sounds more like it would slip smoothly into a lock, key or Schlüssel? Now tell me what tones detective, private eye, and sleuth have for you.
But where does this word come from, sleuth? Ah, well, there’s an interesting trail. And it’s a trail that can’t be pursued without sloth. You see, sloth is the older form of this word. But this sloth is not related to the word sloth that we know and use today; that word comes from slow+th just as width comes from wide+th. But it happens that the modern word sloth also used to have a form sleuth, so it seems that the shift from sloth to sleuth is a more natural one than some might expect. (It’s easier if you’re an armchair sleuth.) Anyway, the sloth that our sleuth comes from is from an Old Norse word for ‘track’ or ‘trail’. That is what a sleuth (sloth) first was: the trail of an animal… or person.
And if you are tracking a person or animal, you may find it useful to have a bloodhound. What, since the 1400s (though less so today), is another name for a bloodhound? Sleuth-hound. It was not until the mid-1800s that persons who tracked other persons came to be called sleuth-hounds. But it took a mere couple of decades for that to be shortened to sleuth. The term was used for fictional detectives at least 15 years before the appearance of Sherlock Holmes (the Oxford English Dictionary has an 1872 citation naming a story called Sleuth, the Detective).
Was sleuth applied to Sherlock Holmes by his author? In “The Red-Headed League,” we see this: “his gently smiling face and his languid, dreamy eyes were as unlike those of Holmes the sleuth-hound, Holmes the relentless, keen-witted, ready-handed criminal agent, as it was possible to conceive.” That appears to be the one and only use of the term in Arthur Conan Doyle’s works (at least that I can find from sniffing around in the Project Gutenberg library), and that’s a sleuth-hound. But that’s not so surprising if you know that the use of the word sleuth for a detective first came about in America. And its use as a verb meaning ‘ply the trade of a detective’ appeared at the beginning of the 1900s.
So there it is: the fruits of amateur armchair sleuthing… a small amount of digging but mostly just looking things up. But the tasting is still up to you.