Definition from Wiktionary, the free dictionary
stiffy (plural stiffies)
- (vulgar, slang) An erection of the penis.
- Fred's got a bulge in his pants - you can tell he's got a stiffy.
- (South Africa) A computer floppy disk of the kind supplied in a stiff plastic outer shell.
- Never leave home without a spare stiffy disc in your bag.