borrowed from Latin -āceus
"having the nature of," extended form of -eus,
going back to *ei̯os
Latin -āceus is an extension of the suffix -eus, meaning "being made of, consisting of," usually applied to a noun designating a material (aureus, argenteus, etc.). Earlier attested derivatives, from Cato and Varro, are from names of plants or plant-based substances (hederāceus, cf. hedera "ivy"; mustāceus/mustāceum "cake made with must (mustum) and ivy leaves"; vīnāceus "refuse from wine pressing"; bētāceus, cf. bēta "beet"; farrāceus, cf. farr, farris "emmer"; lolleāceus, cf. lolium "darnel." Contrasting with these are the jocular formations gallīnāceus ("of poultry"; cf. gallīna "hen") and Gēryonāceus (cf. Gēryōn, a mythical monster) in Plautus. The origin of the -āc- formative is uncertain. It has been suggested that the basis was re-segmentation of a hypothetical *portulāceus, from portulāca, "purslane"—something of a stretch, though it does point to the possible relevance of -ācus or -āca as a suffix itself.