-trum

Etymology
In inherited words, from, from. In words borrowed from Greek (and possibly in some neologisms), from, which is a cognate of the Latin ending. Ultimately from the same source as, , , , which seem to have originated as contextual variants of a single suffix.

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


 * when the directly preceding sound is /s/. (The instrument noun suffix seems not to occur in this context.) Examples:, ,.
 * when the stem contains /r/ or /l/ (in any position). Examples:, . The use of -trum in this context seems to be a feature of old formations inherited from Proto-Indo-European (such as , from ). However, -trum is not obligatory in this context: the suffix -culum may be found after /r/, and  (a dissimilated variant of -culum) may be found after /l/. Instrument nouns in (...)r...culum or (...)l...crum may represent more recent formations than those in  (...)l/r...trum.

The corresponding Ancient Greek ending enjoyed a wider use, and some Greek words with this ending were adapted in ancient times as Latin words ending in -trum, such as  (from Greek ) and  (from Greek ).

In addition, the ending -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 the word, from , 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.
 * In New Latin, -trum has regained some productivity and popularity as a means of forming neuter instrument nouns, apparently influenced by analogy with the masculine agent noun suffix and the way that suffixes descended from it are used in certain modern languages to form inanimate nouns. For example, the New Latin terms  and  have been coined for 'computer' by partial analogy with words such as Spanish  and French . Other New Latin coinages in -trum include  and, adapted from corresponding words in modern languages such as English  and . In effect,  is treated by some New Latin authors as a neuter version of the agent noun suffix , similar to how  serves as its feminine equivalent (despite the fact that in classical Latin, masculine agent nouns in  only rarely have a corresponding neuter noun in ).