-isso

Borrowed from Ancient Greek -ίζω (-ízō), possibly via a variant -ίσσω that existed in the dialect of Tarentum in Southern Italy (as in σαλπίσσω, λακτίσσω).^[1]

-issō (present infinitive -issāre, perfect active -issāvī, supine -issātum); first conjugation

1. Used to form similative verbs from nouns and adjectives.

• This form of the suffix occurs mainly in the comedies of Plautus, written at a time before the use of the letter Z in Latin words loaned from Greek was firmly established. In later time periods, the usual spelling became -izō (a variant -idiō also developed).^[2]

¹At least one use of the archaic "sigmatic future" and "sigmatic aorist" tenses is attested, which are used by Old Latin writers; most notably Plautus and Terence. The sigmatic future is generally ascribed a future or future perfect meaning, while the sigmatic aorist expresses a possible desire ("might want to"). It is also attested as having a rare sigmatic future passive indicative form ("will have been"), which is not attested in the plural for any verb.
²The present passive infinitive in -ier is a rare poetic form which is attested.