So, in $hash{ $w1 }->{ $w2 }->{ words } (which can be written more concisely without the unnecessary arrows - $hash{ $w1 }{ $w2 }{ words }) you have a reference to a hash. And you want to get all of the keys from that hash. So use the keys function. Only slight complexity is that 'keys' takes a hash as a parameter, not a hash reference. So you need to dereference your reference.

@newarray = keys %{ $hash{ $w1 }{ $w2 }{ words } };
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Update: s/values/keys/g

Update: On re-reading your question, I think that BrowserUk has understood it better than me.

Update: Fixed doc link.