Here are a few interpretations:
* Opposite in meaning: The opposite of starting with double letters would be ending with double letters.
* Opposite in function: If you're thinking of a process, the opposite of starting with double letters could be removing double letters.
* Opposite in terms of a task: If you're given a task to find words starting with double letters, the opposite task would be to find words ending with double letters or find words that don't have double letters.
To give you a more specific answer, could you please clarify what you mean by "opposite" in this context?