According to a Danish grammar text, the adverb ret means rather. However, at the time of writing the Duo hints mention pretty and very.
Ret is an amplifier - it amplies or strengthens the meaning of an adjective or another adverb. The grammar text lists some amplifiers:
- alt for = far too
- ganske = absolutely, quite
- meget = very
- ret = rather
Source: 2000 edition of Danish: An Essential Grammar (numbered page 109 of text, PDF page 124 of 225).
On the web it's quite easy to find a PDF of Danish: An Essential Grammar by Allan, Holmes and Lundskaer-Nielsen (edition published 2000). A preview of the 2015 edition of Danish: A Comprehensive Grammar is available in g00glebooks.