A unit of measurement is a definite magnitude of a physical quantity.

A bitcoin is a unit for an amount of bitcoins.   It sounds like a tautology, but it's not.   A satoshi (10e-8 bitcoins) is an other unit for the amount of bitcoins.    Had satoshi called his system "bitgold", he could have called the standard unit a "bitgram" for instance.  Things would maybe have been clearer.   He did not, so that might confuse some.  The thing is that there is no other word to call the "electronic substance" that can be transferred with the bitcoin software.


Whether bitcoins as a whole can be used as a measurement for value (in the sense "commercial value") is a very different matter.  Whether it is true or not does not change the fact that bitcoin is indeed a unit.