Perhaps ultimately from the nominative masculine singular of oppositional adjectives in Proto-Indo-European *-teros; perhaps extended from the suffix in prepositions like inter, praeter.
-iter (comparative -ius, superlative -issimē)
- -ly; used to form adverbs from adjectives.
The suffix -iter is usually added to a third-declension adjective stem to form an adverb of manner.
- adverbiāliter (“adverbially”), from adverbiālis (“adverbial”)
- celeriter (“swiftly, immediately”), from celer (“fast, swift”)
- fortiter (“strongly, powerfully”), from fortis (“strong, powerful”)
- nātūrāliter (“naturally”), from nātūrālis (“natural”)
The suffix -iter was sometimes added to a second-declension stem, although -ē and -ō were more commonly used in such situations.
- avāriter (“greedily”), from avārus (“greedy”)
- circiter (“round about”), from circus (“circle”)
- dūriter (“roughly, harshly”), from dūrus (“rough, harsh”)