D’ror is a very strange word to use for liberty. The Targum Onkelos renders it as cherut, a more usual word for freedom. The sages offer various linguistic analogies, such as a connection with ladur, “to dwell”, since a person with liberty can chose how and where to dwell. Another rabbinic view links it with a noun, d’ror, a swallow, a bird which sings when it is free but not otherwise.
If we take it that the word has a three-letter root, d-r-r, there is an underlying meaning of “to stream, to flow” – which enables us to see the word in our verse as indicating being unhampered, unhindered, unrestrained.
A person or nation blessed with d’ror in this sense is master of their own destiny.