The adverb "twice," meaning "two times," "on two occasions," or "doubly," has its origins in Old English and reflects a clear morphological and phonological development within the Germanic branch of the Indo-European language family. Its earliest attested form is found in Old English as "twīges" or "twīwa," which functioned as an adverbial expression denoting the concept of "twice" or "doubly." This form was constructed from the base numeral "twā," meaning "two," combined with the adverbial genitive suffix "-es."
The base "twā" itself is the Old English feminine nominative and accusative form of the numeral two, which is inherited from Proto-Germanic *twō. This Proto-Germanic form is in turn derived from the Proto-Indo-European root *dwóh₁, the dual form of the numeral two, which is well-attested across Indo-European languages. The numeral "two" and its derivatives are thus inherited cognates, not borrowings, tracing back to the earliest stages of the Germanic languages and beyond.
The suffix "-es" in Old English served as a genitive ending, which, when applied adverbially, formed expressions indicating "in the manner of" or "to the degree of" the base word. In the case of "twīges," the genitive suffix transforms the numeral "two" into an adverbial form meaning "two times" or "twice." This morphological process is typical of Old English adverb formation, where genitive forms of nouns or numerals were used to express frequency or manner.
By the Middle English period, around the 12th to 14th centuries, the form "twies" was commonly used, reflecting the phonological and orthographic changes characteristic of the transition from Old to Middle English. The vowel and consonant shifts, as well as the simplification of inflectional endings, led to the loss of the original genitive "-es" as a distinct morpheme, though it remained orthographically present.
In the 15th century, the spelling of "twies" shifted to "twice," a change motivated by the desire to preserve the /s/ sound at the end of the word. This orthographic adjustment parallels the development of the related adverbs "once" and "thrice," which similarly evolved from Old English "ānes" and "þrīwes," respectively. The pattern "once, twice, thrice" thus forms a complete set of adverbs indicating frequency, each derived from the corresponding Old English numeral plus the genitive suffix, with the "-ice" spelling emerging in Middle to Early Modern English to maintain phonetic clarity.
It is noteworthy that no analogous "-ice" forms exist for numerals beyond three; for example, "four times" is expressed periphrastically rather than as a single adverbial word. This limitation suggests that the formation of these adverbs was lexicalized specifically for the first three numerals, possibly due to their frequent use and the phonological constraints of the language.
In summary, "twice" is an inherited Germanic adverb formed in Old English by combining the numeral "twā" (two) with the adverbial genitive suffix "-es," resulting in "twīges" or "twīwa." This form evolved through Middle English "twies" to the modern spelling "twice" in the 15th century, aligning with a broader pattern seen in "once" and "thrice." The etymology of "twice" is firmly rooted in the inherited Indo-European numeral system and Old English morphological processes, with no evidence of later borrowing influencing its development.