சி.டி. (Si.Di.) This is the most common way to say CD in Tamil. It is the abbreviation for "Compact Disc".
சிடி (SiDi) This is a shorter version of the abbreviation, leaving out the period.
ஒருங்கிணைந்த வட்டு (orungginaidha vattu) - This translates to "integrated disc" and is a more descriptive, but less commonly used term.
The choice of which term to use depends on the context and the speaker's preference.