Here are some options, depending on the context:
For "extend" meaning to make longer or wider:
* Extensively: This emphasizes the breadth or scope of the extension.
* Widely: Similar to "extensively," but emphasizing the spread of the extension.
* Considerably: Implies a significant amount of extension.
* Significantly: Similar to "considerably," but with a slightly more formal tone.
* Broadly: Indicates a wide range or scope of extension.
For "extend" meaning to offer something:
* Generously: Indicates a willingness to offer something freely and abundantly.
* Kindly: Indicates a friendly or helpful offer.
* Courteously: Emphasizes politeness and respect in the offer.
For "extend" meaning to last or continue:
* Continuously: Indicates something lasting without interruption.
* Indefinitely: Suggests something lasting for an unknown or very long period.
* Permanently: Implies something lasting forever or for a very long time.
The best adverb will depend on the specific meaning of "extend" and the desired nuance.