-tus

Etymology
By analogy with derivatives of verbs ending in  and, which are plenty.

Suffix

 * 1)  forms nouns from verbs, describing an action or event

Usage notes
This variant of the suffix is used when the verb belongs to the conjugation classes:
 * 66 (rohkaista); the stem for the verb will be the consonant stem ending in -s-
 * 69 (valita); the stem for the verb will be the part prior to the final -ts-

Etymology 1
From, from.

Compare 🇨🇬, 🇨🇬,.

Usage notes
Verb stems may be modified by the attachment of this suffix in certain predictable or unpredictable ways:
 * Stem-final b and g are regularly devoiced to p and c respectively. If the stem ends in a short vowel directly followed by g, this vowel is usually lengthened (due to Lachmann's Law) but sometimes remains short (especially after the high vowel i, as in cōnstrictus from cōnstringō or fictus from fingō).
 * Stem-final qu is delabialised, giving c. Likewise, stem-final ngu is delabialized to nc.
 * Stem-final v either merges with the preceding vowel (yielding the diphthong au in the case of -av-, or the long vowels ō and ū in the case of -ov- and -uv-/-u-) or is replaced with c. These are the expected outcomes of the distinct Proto-Italic consonants *w and *gʷ, respectively, which merged between vowels in Latin as -v-. However, Latin c in this context does not always descend from original Proto-Italic  *gʷ, because analogical changes took place after the merger and affected the distribution of c.
 * Stem-final d or t fuses with the t of the suffix, giving . This is simplified to if not preceded by a short vowel. Similarly to g-final stems, d-final stems sometimes (but not always) have lengthened vowels in the past participle due to Lachmann's Law.
 * Stem-final rg also fuses with the t, giving.
 * Stem final ll or rr sometimes fuses with the t, to and  respectively.
 * When attached to stems of 1st, 2nd or 4th conjugation verbs, the long vowel at the end of the present stem may be either retained unchanged, replaced by short -i-, or dropped entirely. It's retained for most 1st conjugation verbs, while it becomes short i for many 2nd conjugation verbs:
 * Stem-final d or t fuses with the t of the suffix, giving . This is simplified to if not preceded by a short vowel. Similarly to g-final stems, d-final stems sometimes (but not always) have lengthened vowels in the past participle due to Lachmann's Law.
 * Stem-final rg also fuses with the t, giving.
 * Stem final ll or rr sometimes fuses with the t, to and  respectively.
 * When attached to stems of 1st, 2nd or 4th conjugation verbs, the long vowel at the end of the present stem may be either retained unchanged, replaced by short -i-, or dropped entirely. It's retained for most 1st conjugation verbs, while it becomes short i for many 2nd conjugation verbs:
 * Stem-final d or t fuses with the t of the suffix, giving . This is simplified to if not preceded by a short vowel. Similarly to g-final stems, d-final stems sometimes (but not always) have lengthened vowels in the past participle due to Lachmann's Law.
 * Stem-final rg also fuses with the t, giving.
 * Stem final ll or rr sometimes fuses with the t, to and  respectively.
 * When attached to stems of 1st, 2nd or 4th conjugation verbs, the long vowel at the end of the present stem may be either retained unchanged, replaced by short -i-, or dropped entirely. It's retained for most 1st conjugation verbs, while it becomes short i for many 2nd conjugation verbs:
 * Stem final ll or rr sometimes fuses with the t, to and  respectively.
 * When attached to stems of 1st, 2nd or 4th conjugation verbs, the long vowel at the end of the present stem may be either retained unchanged, replaced by short -i-, or dropped entirely. It's retained for most 1st conjugation verbs, while it becomes short i for many 2nd conjugation verbs:
 * Stem final ll or rr sometimes fuses with the t, to and  respectively.
 * When attached to stems of 1st, 2nd or 4th conjugation verbs, the long vowel at the end of the present stem may be either retained unchanged, replaced by short -i-, or dropped entirely. It's retained for most 1st conjugation verbs, while it becomes short i for many 2nd conjugation verbs:
 * When attached to stems of 1st, 2nd or 4th conjugation verbs, the long vowel at the end of the present stem may be either retained unchanged, replaced by short -i-, or dropped entirely. It's retained for most 1st conjugation verbs, while it becomes short i for many 2nd conjugation verbs:

Noun stems generally do not exhibit these modifications; there are some adjectives ending in -stus that originate from s-stem nouns, such as, , but overall the suffix is rarely found attached directly to a consonant-final noun stem. Most derivatives in -tus from nouns include a long vowel before the -t-, which may in some cases originate partly or wholly from the final vowel of the stem (for example, from  and  from  ), but which at least eventually was subject to reanalysis as part of the suffix; see, ,.

Etymology 2
From, from.

Compare 🇨🇬, 🇨🇬, 🇨🇬.

Usage notes
The verb stem undergoes the same modifications as for the participle suffix; see.

Etymology 3
From. Compare 🇨🇬, 🇨🇬. See.

Usage notes
Same as for the participle suffix.

Etymology 4
From. Compare 🇨🇬, found in the adverb, and 🇨🇬, found as an ablatival ending in ,.

Suffix

 * 1)  -ly;