What does ostreātus mean in Latin?

ostreātus, a adjective, means “rough, scabby”.

How do you pronounce ostreātus?

In classical Latin, [ɔs.treˈaː.tʊs]; in ecclesiastical (church) Latin, [os.treˈaː.tus].

adjectivefirst/second-declension adjective

ostreātus (feminine ostreāta, neuter ostreātum)

Classical[ɔs.treˈaː.tʊs]Ecclesiastical[os.treˈaː.tus]

adjectiverarerough, scabby
[…]itaque iam quasi ostreatum tergum ulceribus gestito / propter amorem vestrum.1912 translation by Henry Thomas Riley. (The Comedies of Plautus. London. G. Bell and Sons. Perseus.) MILPHIO: as it is, I've already got my back about as hard with weals as an oyster-shell, by reason of your amours.c. 194 BCE, Plautus, Poenulus 1.2.191–192

singular
form	masculine	feminine	neuter
nominative	ostreātus	ostreāta	ostreātum
genitive	ostreātī	ostreātae	ostreātī
dative	ostreātō	ostreātae	ostreātō
accusative	ostreātum	ostreātam	ostreātum
ablative	ostreātō	ostreātā	ostreātō
vocative	ostreāte	ostreāta	ostreātum

plural
form	masculine	feminine	neuter
nominative	ostreātī	ostreātae	ostreāta
genitive	ostreātōrum	ostreātārum	ostreātōrum
dative	ostreātīs	ostreātīs	ostreātīs
accusative	ostreātōs	ostreātās	ostreāta
ablative	ostreātīs	ostreātīs	ostreātīs
vocative	ostreātī	ostreātae	ostreāta

ostrĕātus, a, um, adj. id.; qs. covered with oyster-shells; hence, transf.,

I. rough, scabby: quasi ostreatum tergum ulceribus (i. e. verberibus), Plaut. Poen. 1, 2, 186.

From ostrea (“oyster”) + -ātus; i.e. "like the shell of an oyster".