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sem-

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Etymology and origin of the Latin word sem-

sem-1 one

Confidence
Established
Formation
Inherited
First attested
c. 250–184 BC, Plautus
Inherited from
Proto-Indo-European *sm-
Ultimate origin
Proto-Indo-European *sm-

Forms

sem-, sim-[1]

Etymology

The prefix “one” is inherited from Proto-Indo-European *sm- (“one”), the form the root of “one” takes in compounds.[1][2] It is no longer a word of its own and appears only as the first part of compounds and derivatives such as semper “always”, semel “once” and simplex “simple”.[1][3] De Vaan reconstructs *sm̥-per “once and for all” and *sm̥-plo- “single” for Proto-Italic.[1]

Cognate with Sanskrit सकृत् (sakṛ́t, “once”) and Ancient Greek ἅπαξ (hápax, “once”).[1][3]

Earliest recorded meaning

It is found from Plautus on, in words such as simplex and simplus.[1]

Meanings

Prefix

  1. One, once, single: semper, semel, simplex, simplus, simītū “at the same time”.[1][3]

Word family

sem-2 half

Confidence
Established
Formation
Derivation
Ultimate origin
Proto-Indo-European *sēm-i

Pronunciation

  • Classical: [ˈseː.m][4]
  • Ecclesiastical: [ˈsɛː.m][4]

Forms

sēm- [4]

Etymology

The prefix “half” is from Latin sēmi- (“half”), the form it takes before vowels.[1][4] That prefix goes back to Proto-Italic *sēmi- and Proto-Indo-European *sēm-i (“in one”), a locative; de Vaan explains the meaning as having shifted from “in one” to “one of the two” and then to “half”.[1]

Cognate with Sanskrit सामि (sāmí), Ancient Greek ἡμι- (hēmi-) and Old High German sāmi-, all meaning “half”.[4][1]

Meanings

Prefix

  1. (before vowels) half: sēmūncia, sēmustus, sēmermis, sēmanimis.[1][4][3]

Word family

Usage notes

De Vaan derives the prefix “half” from the same root as the prefix “one”.[1] Before ⟨m⟩ the prefix “half” is sometimes reduced to sē-, as in sēmodius.[1] The OLD lists the forms sēmermis, sēmanimis and sēmustus under their fuller spellings with sēmi-.[3]

References

  1. ^ a b c d e f g h i j k l m de Vaan, Michiel (2008), Etymological Dictionary of Latin and the other Italic Languages, Leiden Indo-European Etymological Dictionary Series 7, Leiden; Boston: Brill
  2. ^ Pokorny, Julius (1959), Indogermanisches etymologisches Wörterbuch, Bern; Munich: Francke
  3. ^ a b c d e Glare, P. G. W., ed. (2012), Oxford Latin Dictionary, 2nd ed., Oxford: Oxford University Press
  4. ^ a b c d e f Wiktionary, the free dictionary, https://en.wiktionary.org

Derived terms

Related etymologies

  • quis · also from Proto-Indo-European
  • cum · also from Proto-Indo-European
  • ego · also from Proto-Indo-European
  • is · also from Proto-Indo-European
  • hic · also from Proto-Indo-European
  • in · also from Proto-Indo-European
  • qui · also from Proto-Indo-European
  • et · also from Proto-Indo-European
Cite this entry

“Sem-.” Etymologically, 23 Oct. 2026, etymologically.com/la/sem-. Accessed 23 Oct. 2026.

Last edited on . ·