General synonyms:
* Extensive: Implies a large area or scope
* Prolonged: Emphasizes the duration of something
* Extended: Similar to prolonged, suggesting a stretching out in time
* Durable: Refers to something lasting a long time
* Enduring: Implies something that continues for a long time, even in the face of challenges
* Lengthy: Formal synonym for "long"
More specific synonyms:
* Tall: For height
* Vast: For distance or size
* Wide: For breadth
* Deep: For depth
* Remote: For distance in time or space
* Ancient: For something very old
* Eternal: For something without an end
Informal synonyms:
* Big: A casual replacement for "long"
* Huge: Implies something very large
* Massive: Similar to "huge" but more formal
* Forever: Emphasizes the indefinite duration of something
It's important to choose the word that best fits the context and the desired meaning.