Dictionary.com doesn't even have the word "ept" listed on its website. That's why ept is the sister of a orphan negative, inept. Logically the two must both exist for either to exist. Inept remains an unpaired word as a result. You can blame ept for orphaning inept... That, or the human race orphaned the word inept by limiting the use of the word ept out of existance. (Proof of this being the fact that if you Google "ept" you will find pregnancy tests offered to you.) You never hear the word "ept" used, ever. That's why inept is the orphan negative.
The Oxford English Dictionary mentions that ept is "Used as a deliberate antonym of ‘inept’: adroit, appropriate, effective."
Ept is synonymous to adept. And since it is the positive form of inept, and is not used in standard practice any more, it is an example of a positive phrase that remains elusive to the English language. While it's negative counter part is used by everyone.
"...there was never a word ept of which (inept) was the negative form. It was actually formed from the Latin ineptus, “unsuited, absurd, foolish”, at the beginning of the seventeenth century. However, it just scrapes a place because ept was created from it in modern times (by E B White of the New Yorker in 1938) and it turns up from time to time in humorous or deliberately incongruous contexts, as do its derived forms eptly and eptitude." (World Wide Words)
I am now ept at using the word ept because I wrote a sentence using the word ept.
Or...
I am now inept at using the word ept because I wrote a sentencing using the word ept.