What is a prefix for competent?

There isn't a single, universally accepted prefix for "competent." However, depending on the specific nuance you want to convey, you could use:

* In-: This prefix indicates "not," so "incompetent" means lacking in competence.

* Un-: Similar to "in-", this prefix also implies "not," resulting in "uncompetent," which signifies a lack of competence.

* Non-: Another prefix meaning "not," "non-competent" emphasizes the absence of competence.

* Im-: Although less common, "imcompetent" is occasionally used to signify a lack of competence.

The choice of prefix depends on the context and the desired level of formality. "Incompetent" is the most common and widely understood term.