As3-sdk is a project mainly written in ACTIONSCRIPT and JAVASCRIPT, it's free.
Wordnik AS3 SDK
Please see http://developer.wordnik.com for additional details on this SDK. This SDK provides access to all of Wordnik's public REST APIs from programs written in Adobe Flash and Flex.
Provided in the Wordnik AS3 SDK is a compiled SWC file, sample code, and documentation. Please take a look at the sample code in the examples folder.
To use the sample code, please edit the Credentials.as and enter your API key, Wordnik username and password. The username and password are only required for testing the Word Lists and authentication features and are not required in your application unless you're working with those.