-undus

Latin

Etymology

Possibly from Proto-Italic *-ontnos, syncopated from *-ontinos, from Proto-Indo-European *-ont- (participial suffix) + *-i- (abstract noun-suffix) + *-nós (adjective-forming suffix), or from Proto-Indo-European *-ótr̥. The -undus suffix, first associated with intransitive deponent verbs as sequor (secundus), orior (oriundus), lābor (lābundus), and other relics, then transitioned from a derivative to an inflectional category, and the gerundive assumed its canonical shape and function.

The sense of necessity (“needing to be read,” etc.) was a pragmatic outgrowth of the more basic meaning: a book that is readable or “disposed” to be read is one that probably should be read.

As with the present participle, the vowel before -n- varies depending on the conjugation class of the verb. All first-conjugation verbs use -andus and all second-conjugation verbs use -endus. Verbs of the third and fourth conjugations show variation between (i)-undus (derived from PIE o-grade) and -(i)-endus (derived from PIE zero-grade), with the latter form dominant by Classical Latin, though not as completely as in in the present participle: older Latin still has vertundus, legundus, etc. Compare the even rarer relics of o-grade vocalism in the present participle, such as the oblique stem eunt- of iēns and the stem volunt- preserved in the noun voluntās.

The derivation from gerundive to the later gerund could then be as easy as an abstraction from “ad librum legendum” (“to the book to be read”) to “ad legendum” (“in order to read”).^[1] Compare -bundus and -cundus.

Pronunciation

(Classical Latin) IPA^(key): [ʊn.dʊs]
(modern Italianate Ecclesiastical) IPA^(key): [un.dus]

Suffix

-undus (feminine -unda, neuter -undum); first/second-declension suffix

derives adjective nouns from verbs, similar to present participles, but without the present time restriction
sequor (“follow”) → secundus (“following”)

orior (“rise”) → oriundus (“rising, originating”)

lābor (“glide, slide, fall”) → lābundus (“falling”)

rotō (“turn around, roll”) → rotundus (“rolling”)
Old Latin or archaic ending of the future passive participle (gerundive) of third- and fourth-conjugation verbs; also classically retained in the following legal set phrase:
pecuniae repetundae ― bribery (beside classical repetendus)

Declension

First/second-declension adjective.

	masculine	feminine	neuter	masculine	feminine	neuter
	singular			plural
nominative	-undus	-unda	-undum	-undī	-undae	-unda
genitive	-undī	-undae	-undī	-undōrum	-undārum	-undōrum
dative	-undō	-undae	-undō	-undīs
accusative	-undum	-undam	-undum	-undōs	-undās	-unda
ablative	-undō	-undā	-undō	-undīs
vocative	-unde	-unda	-undum	-undī	-undae	-unda