Tmesis is a linguistic phenomenon in which a word or set phrase is separated into two parts, often with other words occurring between them, usually for emphatic, and/or humourous effect. In theory, some would say that Tmesis is only an accurate description of words that are compound words originally, and are divided between the original root words that were compounded, however in practice the process is used with many words that are not compounded, though normally the division is at a syllable or morpheme boundary. If divided at a syllable boundary which is not a division between roots which may have gone into forming a compound word, it may be more exact to call it Dystmemsis. Some consider the simple breaking of a word into two parts without adding additional words, phrases or syllables between to also be Tmesis, such as "In Between" and "In Sane" for emphasis or meter. Tmesis is an type of rhetorical scheme (Schemes in Linguistics are systems of word usage and/or word organization, that deal with word order, syntax, letters, and sounds, rather than the systems dealing with the meanings of words, which are covered under the designation: Tropes.). Originally Tmesis was said to be a basic component of Archaic Greek, however, now there is much disagreement over that characterization, since it may be that in early Archaic Ægean Language the prefixes may not have reached a stage where they were already combined with the other root word to form nouns and/or verbs and so forth, so to speak of dividing a compound word in that situation may be sort of "cart before horse"ish. Temesis is also sometimes referred to as 'Tumbarumba', possibly due to the popularity of Tmesis in Australian speech (Tumbarumba being an Australian town), or possibly due to the poem "Tumba Bloody Rumba" by John O'Grady, which includes several Tmeses including "Tumba-bloody-rumba", "e-bloody-nough", and "kanga-bloody-roos"
A variant type of infixion perhaps, Tmesis became extremely popular in the late 1960s and the 1970s in American Culture, from Haight Ashbury to Rowan & Martin's Laugh-In. Some of the most popular instances, "Far-Fucking-Out", "Fan-Fucking-Tastic", "Abso-Fucking-Lutely", and so forth were primarily markers of indifference to the affectations of decorum by the previous "mainstream" culture, which however fictitious in reality (even in its heyday), was in the process of being replaced. At any rate, these example do fall into the Expletive Infixion category.
Often when the expletive is inserted it may be contracted such as Fuckin for Fucking, etc., and frequently toned-down euphemisms are utilized such as in: La-dee-freakin'-da"
The term, Tmesis comes from Archaic Greek τμῆσις (tme-sis), meaning "a cutting" and τέμνω (temno-), meaning "I cut")
Shakespeare, in Troilus and Cressida, writes the phrase, "how dearly ever parted" (III.iii), when we would expect to find the phrase written as "however dearly parted" in normal grammatical usage. Goldwyn once wrote, "I have but two words to say to your request: Im Possible." In the movie True Lies, one character states, "I have two words to describe that idea. In Sane." Milton writes, "Which way soever man refer to it." The poet W. H. Auden makes emotionally laden use of tmesis in "Two Songs for Hedli Anderson," where he stretches out the word forever by writing: "I thought that love would last For Ever. I was wrong." In English, this rhetorical scheme is fairly rare, since only the compounds of "ever" readily lend themselves to it, but it is much more common in Greek and Latin. An exception to this generalization is the American poet e. e. cummings (the lack of capitalization in his name is a rhetorical affectation). Critics note that cummings makes particularly potent use of tmesis in poems like "she being Brand / -new", in which words like "brand-new" and "O. K" are artificially divided across separate lines of text to create an unusual, broken reading experience. Particularly clever poets may use a sort of infixation to insert other words of phrases between the two parts that have been split apart. For instance, a southerner might say, "I live in West--by God--Virginia, thank you very much!"
One example of a case where a phrase is inserted rather than a word occurs in the "Legen-wait for it-dary", in which the phrase "wait for it" is inserted into the word Legendary. This phrase was popularized by the character Barney Stinson on the television series How I Met Your Mother.