-ter

• -iter, -er

Perhaps ultimately from the nominative masculine singular of contrastive adjectives in Proto-Indo-European *-teros, later used more generally; perhaps extended from the suffix in prepositions like inter, praeter. Cognate with Ancient Greek -τερος (-teros).

• (Classical Latin) IPA^(key): /ter/, [t̪ɛr]
• (modern Italianate Ecclesiastical) IPA^(key): /ter/, [t̪er]

-ter (comparative -tius, superlative -tissimē)

1. -ly; used to form adverbs from adjectives.

The suffix -ter is usually added to a third-declension adjective or participle stem to form an adverb of manner.

Adjectives with a nominative singular in -ns and genitive singular in -ntis form adverbs in -nter rather than in *-ntiter, such as prūdenter (“intelligently, wisely”), from prūdēns (“knowing, experienced”): this can be considered a form of haplology. Other third-declension adjectives generally form adverbs in -iter, such as celeriter (“swiftly, immediately”) from celer (“fast, swift”). The -i- before the -ter can be analyzed either as part of the suffix (dividing the word as celer-iter, where -iter is an allomorph of -ter) or as part of the adjective's stem (dividing the word as celeri-ter, where -i- is the stem-final vowel seen also in some inflected forms like the neuter nominative/accusative plural celeri-a). Alternatively, -i- in this context can be analyzed as a connecting vowel that comes between the stem and the suffix.^[1][2]

Further examples of regularly formed adverbs:

dissimulanter (“dissemblingly, secretly”), from dissimulāns, present active participle of dissimulō (“dissemble, conceal”)

adverbiāliter (“adverbially”), from adverbiālis (“adverbial”)

fortiter (“strongly, powerfully”), from fortis (“strong, powerful”)

nātūrāliter (“naturally”), from nātūrālis (“natural”)

There are only a few adverbs formed without -i- from adjectives not ending in -ns, -ntis:

audācter (“boldly, audaciously, fearlessly”), from audāx (“bold, audacious, daring”)

simulter, from similis

faculter, difficulter, indifficulter, from facilis, difficilis

sollerter, sōlerter, from sollers, sōlers

inerter, from iners

The suffix -iter was sometimes added to a second-declension stem, although -ē and -ō were more commonly used in such situations.

Examples:

avāriter (“greedily”), from avārus (“greedy”)

circiter (“round about”), from circus (“circle”)

dūriter (“roughly, harshly”), from dūrus (“rough, harsh”)

• (-ly): -ē, -ō

• Old Occitan: -tre (possibly)

• -der

From Proto-Celtic *-teros (comparative suffix^[1]),^[2] from Proto-Indo-European *-teros. Cognate with Cornish -ter.

• (North Wales, standard, colloquial) IPA^(key): /tɛr/, /dɛr/
  • (North Wales, colloquial) IPA^(key): /tar/, /dar/
• (South Wales) IPA^(key): /tɛr/, /dɛr/

/tɛr/ and /dɛr/ are variants of the same suffix. /tɛr/ (phonetically [tʰɛr]) is always spelt -ter whereas /dɛr/ is represented by -ter after an unvoiced fricative (phonetically [tɛr]) and by -der after other voiced sounds (phonetically [dɛr]).

-ter m (plural -terau)

1. forming abstract nouns, -ness, -ment

   ‎craff (“observant, astute”) + ‎-ter → ‎craffter (“astuteness”)

   ‎gwag (“empty”) + ‎-ter → ‎gwacter (“emptiness”)

   ‎pell (“far”) + ‎-ter → ‎pellter (“distance”)

• R. J. Thomas, G. A. Bevan, P. J. Donovan, A. Hawke et al., editors (1950–present), “-ter”, in Geiriadur Prifysgol Cymru Online (in Welsh), University of Wales Centre for Advanced Welsh & Celtic Studies