It's not a plural, it's the nominative form. The plural form of gyros (in 'scientific' transcription) would be gyroi, but it's never used seeing as it's not a countable word. They. Are. Amazing. My friend brought them yesterday and I've been stuffing my face since I cracked the first one open last night. I have (had) this big 10-kg bag in the kitchen and I was planning at first to make liqueur, but I'm probably going to end up eating them all.