hardening off
n.— «It is best not to put seedling so young directly out in the garden. “Hardening off” is the term for gradually acclimating them to outdoor conditions. I use an half-way house, also known in garden circles as a cold frame, i.e., an enclosed, bottomless box with a clear glass or plastic lid that can be propped open for ventilation or closed against a chilly night.» —“Gardener to tomatoes: Step outside!” by Valerie Sudol Star-Ledger (New Jersey) May 6, 2008. (source: Double-Tongued Dictionary)
Further reading
Secret signals on the job: Waitresses at some 19th-century restaurants ensured speedy drink service by communicating with a non-verbal code. One server took orders, then placed each customer’s cup to indicate exactly what the customer wanted...
The word nurdle, sometimes spelled nerdle, can be used to denote various “small bits of things,” such as styrofoam packing material or detritus in one’s pockets. It may be related to the word nodule. Like thingamabob and whatsit...
This is not a new term. I first heard and read it in the early 1980’s and it is probably older than that.
This meaning is found in the Collins online dictionary.
http://dictionary.reverso.net/english-definitions/harden%20off