The etymological fallacy is a genetic fallacy that holds that the present-day meaning of a word or phrase should necessarily be similar to its historical meaning. This is a linguistic misconception, and is sometimes used as a basis for linguistic prescription. An argument constitutes an etymological fallacy if it makes a claim about the present meaning of a word based exclusively on its etymology. This does not, however, show that etymology is irrelevant in any way, nor does it attempt to prove such.
A variant of the etymological fallacy involves looking for the true meaning of words by delving into their etymologies, or claiming that a word should be used in a particular way because it has a particular etymology. A notable example is the word decimation, which used to refer to reduction by a tenth, but in modern English means reduction by an extreme amount.
An etymological fallacy becomes possible when a word has changed its meaning over time. Such changes can include a shift in scope (narrowing or widening of meanings) or of connotation (amelioration or pejoration). In some cases, meanings can also shift completely, so that the etymological meaning has no evident connection to the current meaning.
For example:
The word hound originally simply meant "dog" in general. This usage is now archaic or poetic only, and hound now almost exclusively refers to dogs bred for hunting in particular.
The meaning of a word may change to connote higher status, as when knight, originally "servant" like German Knecht, came to mean "military knight" and subsequently "someone of high rank".
Conversely, the word knave originally meant "boy" (as the equivalent German Knabe) and only gradually acquired its meaning of "person of low, despicable character".
The word lady derives from Old English hlæf-dige ("loaf-digger; kneader of bread"), and lord from hlafweard ("loaf-ward; ensurer, provider of bread"). No connection with bread is retained in the current meaning of either word.
Not every change in meaning provokes an etymological fallacy, but such changes are frequently the basis of inaccurate arguments.
From the fact that logos is Greek for "word", Stuart Chase concluded in his book The Tyranny of Words that logic was mere manipulation of words.
Some dictionaries of old languages do not distinguish glosses (meanings) from etymologies, as when Old English geþofta is defined as "one who sits on the same rowing bench; companion". Here the only attested meaning is the second one, while the first is simply the word's etymology.
The word apologize comes from the Greek word ἀπολογία (apologia) which originally only meant "a speech in defence". Later on it began to carry the sense of expressing remorse or "saying sorry" over something that one may feel regret for, as well as to explain or defend, in some contexts. The word began to be used eventually as only expressing regret mainly because words of remorse would often accompany explanations, or at least some defense or justification along with it. The word is still sometimes used in its original sense, especially in the form "apologist", meaning someone who explains and justifies a belief.
Phrases such as to grow smaller or to climb down have been criticised for being incoherent, based on the original meanings of grow and climb.
