>Is this a sentence?

That means 'okay' The decision is yours.

Still it needs to be capitalized and punctuated.

@Haydar
"Tamam." şeklinde yazabilirsin. Tırnaklar olmadan...

Yes, it's a perfect sentence.
As indicated by freefighter, it should be capitalized and there should be a full stop at the end.

Düzeltildi.

@soliloquist

"Tamam" comes from the Arabic adverb "tamàman" (تماما) which means "exactly." The colloquial Arabic word "tamàm" is often used in Middle Eastern Arabic dialects like the Syrian dialect which is geographically close to the Turkish language. This might explain why Turkish borrowed it.

The Arabic word comes from the lexical root TMM that also gave the verbs "tamma" (تمّ) which means "to be finished, to end, to come to an end" and "tammama" (تمّم) which means "to finalize, to finish, to end). The adjective "tàmm" (تام) means "finalized, finished, perfect).

I don't know of an Amazigh loanword that comes from this Arabic lexical root. This is a case which shows that Turkish borrowed Arabic words that were not borrowed by Tamazight. In Algerian Arabic, the only word that comes to my mind that was derived from this lexical root is "temtem" which means "right away, immediately" in Algerian Arabic. I'm not sure if the Algerian Arabic word "ltemm" (there) also comes from this root.

Thank you very much for the information.

You're welcome ^^