ostra

oyster

Related: aburrirse como una ostra, champiñón ostra, ostrería, ostrero, salsa de ostras

According to the RAE, borrowed from Portuguese ostra, ultimately from Latin ostrea. But Mackenzie seems to treat this Spanish word as a straightforward inheritance from the Latin word, with the non-breaking of o due to metaphony triggered by the -e-, which became a subsequently-lost glide.