-trum

• -culum, -crum, -tra

In inherited words, from Proto-Italic *-trom, from Proto-Indo-European *-trom. In words borrowed from Greek (and possibly in some neologisms), from Ancient Greek -τρον (-tron, instrument noun suffix), a cognate of the Latin ending. Ultimately from the same source as -culum, -crum, -bulum, -brum, which seem to have originated as contextual variants of a single suffix.

• (Classical Latin) IPA^(key): /trum/, [t̪rʊ̃ˑ]
• (modern Italianate Ecclesiastical) IPA^(key): /trum/, [t̪rum]

-trum n (genitive -trī); second declension

1. suffix forming instrument nouns from verbs

   Synonyms: -culum, -men, -mentum, -tōrium, -ium

While Latin was a living language, this ending was less productive than the instrument noun suffix -culum (etymologically the same suffix). Weiss 2009, citing Serbat 1975, describes -trum as moribund and unproductive after the time of Augustus;^[1] Owens 2016, citing Mir 1984, likewise characterizes -trum as unproductive and "archaic even in the classical period".^[2] In native Latin formations, -trum generally can be found only in the following two circumstances:

• directly after /s/. (The instrument noun suffix -culum seems not to occur in this context.) Examples: mōnstrum, castrum, haustrum.
• when the stem contains /r/ or /l/ (in any position).^[3] Examples: mulctrum, rutrum. However, -trum is not always used in this context: the suffix -culum may be found after /r/, and -crum (a dissimilated variant of -culum) may be found after /l/. The use of -trum in this context may be a characteristic of older formations such as arātrum (inherited from Proto-Indo-European *h₂érh₃trom, albeit with analogical replacement of -a- with -ā-), whereas instrument nouns in (...)r...culum or (...)l...crum may be more recent formations.

The corresponding Ancient Greek ending -τρον (-tron) enjoyed a wider use, and some Greek words with this ending were adapted in ancient times as Latin words ending in -trum, such as scēptrum (from Greek σκῆπτρον (skêptron)) and metrum (from Greek μέτρον (métron)).

In addition, -trum has occasionally been used to derive neologisms from Latin roots outside of the two conditions described above.

• The earliest example of this may be spectrum, from speciō, first attested in antiquity in a pair of letters between Cicero and Cassius Longinus, where it is implied that Catius may have created the word as a translation of the Greek philosophical term εἴδωλον (eídōlon).^[4]
• In New Latin, -trum has become more productive and popular as a means of forming neuter instrument nouns, apparently influenced by analogy with the masculine agent noun suffix -tor and the way that suffixes descended from it are used in certain modern languages to form inanimate nouns. For example, the New Latin terms computātrum and ōrdinātrum have been coined for 'computer' by partial analogy with words such as Spanish computador and French ordinateur. Other New Latin coinages in -trum include mōtrum and monitrum, adapted from corresponding words in modern languages such as English motor and monitor. In effect, some New Latin authors treat -trum as a neuter version of the agent noun suffix -tor, similar to how -trīx serves as its feminine equivalent (despite the fact that in classical Latin, masculine agent nouns in -tor only rarely have a corresponding neuter noun in -trum).

The suffix is typically neuter, but a feminine by-form -tra can be seen in the instrument noun mulctra (also mulctrum), and a masculine by-form -ter can be seen in the instrument noun culter (“knife”) and in arāter, a rare variant form of arātrum (“plough”).

Second-declension noun (neuter).