What is the prefix for word thought?

There isn't a specific prefix for the word "thought." However, there are prefixes used in words related to thought, such as:

* Pre-: meaning before, as in "preconceived" or "premeditated."

* After-: meaning following, as in "afterthought."

* Re-: meaning again, as in "rethink" or "reconsider."

* Mis-: meaning wrongly, as in "misthought" or "misconception."

* Over-: meaning excessively, as in "overthink."

The prefixes used will depend on the specific meaning you want to convey.