opacus

Latin

Unknown. Antonym of aprīcus. Long compared with Proto-Germanic *abuhaz (“turned the wrong way, wicked”), Sanskrit अपाञ्च् (ápāñc, “located backwards, behind”), Serbo-Croatian опак, ȍpāk (“wicked, evil”), which are from Proto-Indo-European *h₂epó (“away”) and Proto-Indo-European *h₃ekʷ- (“see”); the Latin would be via metathesis from *apōcus.^[1]

De Vaan remains unconvinced and suggests Proto-Italic *op-wākos (“situated towards the empty side”), from Proto-Indo-European *h₁epi (Latin ob) and Proto-Indo-European *h₁weh₂- (“empty”) (Latin vacuus and vānus), with the same phonetic development as in oportet.^[2]

opācus (feminine opāca, neuter opācum); first/second-declension adjective

	masculine	feminine	neuter	masculine	feminine	neuter
	singular			plural
nominative	opācus	opāca	opācum	opācī	opācae	opāca
genitive	opācī	opācae	opācī	opācōrum	opācārum	opācōrum
dative	opācō	opācae	opācō	opācīs
accusative	opācum	opācam	opācum	opācōs	opācās	opāca
ablative	opācō	opācā	opācō	opācīs
vocative	opāce	opāca	opācum	opācī	opācae	opāca

“opacus”, in Charlton T. Lewis and Charles Short (1879) A Latin Dictionary, Oxford: Clarendon Press
“opacus”, in Charlton T. Lewis (1891) An Elementary Latin Dictionary, New York: Harper & Brothers
opacus in Gaffiot, Félix (1934) Dictionnaire illustré latin-français, Hachette.

^ Pokorny, Julius (1959) “apo-”, in Indogermanisches etymologisches Wörterbuch [Indo-European Etymological Dictionary] (in German), volume 1, Bern, München: Francke Verlag, pages 54-55
^ De Vaan, Michiel (2008) “opācus”, in Etymological Dictionary of Latin and the other Italic Languages (Leiden Indo-European Etymological Dictionary Series; 7), Leiden, Boston: Brill, →ISBN, page 429