add-in 
noun
A device or piece of software that can be added to a computer to give extra features or functions: add-in boards the latest add-ins...
- But the Power Mac is a special case in that its graphics are add-ins, so Apple can pretty much bundle whatever board takes its fancy.
- Certainly, those machines, with their SDMC add-in slot, new peripheral connector and other refinements, will be high on developers' shopping lists - higher, at any rate, than the older PDAs.
- Intel is also known to be working on an add-in that combines Wi-Fi and 3G mobile phone network connectivity, but it is not expected to unveil this product until later this Autumn.
- shoulder to shoulder
- shouldn't
- shounen
- shout
- shouter
- shouting distance
- shouting match
- shout line
- shout-out
- shout something from the housetops
- shout something from the rooftops
- shout the odds
- shouty
- shove
- shove-halfpenny
- shovel
- shovelboard
- shoveler
- shovelful
- shovel hat
- shovelhead
- shovelhead shark
- shoveller
- shovel pass
- shovel-ready