sleeping giant

/ˈslipɪŋ ˈʤaɪənt/

Other forms: sleeping giants

When you call someone a sleeping giant, you're suggesting that they have a lot of power, especially destructive power, but they're not currently using it.

You'll often hear this phrase in the expression "awaken a sleeping giant." If you were coming in to a giant's house to rob him while he slept, you certainly wouldn't want him to wake up. Similarly, if you awaken a sleeping giant, you've caused a big problem for yourself by activating or drawing the attention of someone or something that was previously dormant.

Definitions of sleeping giant

1. noun

   someone or something whose power or strength is not seen or understood, but who will show unexpected power when provoked