Rack of lamb
The use of rack in this sense comes from the 14th century use of the word meaning a framework, indicating the framework of how the lamb ribs have been presented by the butcher. The same word is used when racking or setting up a display or framework of bottles, snooker balls etc. The same sense is used when clothing is taken ‘off the rack’ or framework, but this usage is much more modern from the 1950s, as is rack meaning a woman’s breasts or ‘framework’, which is US slang from the 1990s. This notion of rack has no etymological association with rack as in the torture device or rack as in something going to rack and ruin.