Bitcoin / Bitcoins / Crypto Currency

Technically you can't 'invest' in a currency.

1. To commit (money or capital) in order to gain a financial return:
   

A currency itself has no means to generate income therefore it provides no return.

You are however correct to call it a speculation call on future outcomes.
I dislike the word 'gamble' because it suggests there are some forms of human decision making that do not involve an assessment of risk over reward.
I do this everytime I cross the road (sometimes Ive called it wrong)