Which word best defines "inept"?

The word "inept" refers to a lack of skill or ability; it describes someone who is awkward or clumsy in their actions. The best word to define "inept" among the given choices is "silly." "Silly" captures a sense of foolishness or ineffectiveness that aligns with the concept of being inept.

While "skillful," "competent," and "brilliant" all indicate a high level of ability or effectiveness, these words directly oppose the meaning of "inept." Thus, "silly," with its connotation of ineptness as being foolish or lacking in seriousness, reflects the essence of inept more closely.