Learn Turkish: Eski tanıdıklara veda ettin mi? - Did you say farewell to the old acquaintances?

The root is tanımak (to know/recognize). By adding the -dık suffix, it typically forms a participle, but here it has become lexicalized. This means tanıdık acts as a normal, standalone noun meaning "acquaintance" and doesn't need any possessive endings. To get tanıdıklara, we just add the plural -lar and the dative case -a (to the acquaintances).

Why is the dative case (-a) used on tanıdıklara?

Because of the verb veda etmek (to say farewell/goodbye). In Turkish, you don't say goodbye "at" or "with" someone; you say goodbye "to" them. Therefore, the object receiving the farewell must take the dative case.

Why is the past tense suffix on the helper verb etmek spelled -tin instead of -din in ettin?

This is a great refresher for consonant assimilation (the "Fıstıkçı Şahap" rule). The verb root et- ends in a voiceless consonant (t). When the past tense suffix -di attaches to it, the d must change to its voiceless pair, t, making it -ti. Finally, we add -n to show it was "you" who did the action.

Is veda etmek used for everyday goodbyes?