Owning or doing anything incurs opportunity cost

There is no other human activity or asset where we call simply owning  and doing nothing with it "Using"

Owning a stock or a commodity or a piece of land somewhere 
and doing nothing with it is a speculative investment (ie it restricts the supply!)
its not a use of the thing.

*Particularly* since Bitcoin has security needs
( Which is the only reason it's valuable anyway )
but the holder doesn't contribute to those.

Nowhere else would we refer to this as "use"