primeval; old; eternal
Doing a quick search, the Pali word 'sanantana' appears to be found rarely in the Pali suttas.
Apart from being used in references to the Vedic (pre-Hindu) teachings about 'Brahma' & 'Eternal Youth' in DN 19, a quick search finds 'sanantana' used in only two Buddhist phrases, as follows:
Saccaṃ ve amatā vācā, esa dhammo sanantano; Sacce atthe ca dhamme
ca, āhu santo patiṭṭhitā.
Truth indeed, is deathless speech — this is the ancient/eternal Dharma. On
truth, its study and practice both, they say are the Peaceful firm.
Most famously in the Dhammapada:
Hatred is never appeased by hatred in this world. By non-hatred alone
is hatred appeased. This is a law eternal.
Na hi verena verāni, sammantīdha kudācanaṃ; Averena ca sammanti, esa
The word 'porāṇaka' appears to be not found in any teachings attributed to the Buddha; however appears found in later-day commentaries & Jataka Tales; as shown in this search list.
The word 'akālika' is supremely important in Buddhism, being one of six attributes of the Dhamma spoken by the Buddha, as follows:
svākkhāto bhagavatā dhammo: perfectly spoken is the Dhamma of the Blessed One
sandiṭṭhiko: visible in the here-&-now
akāliko: immediately effective; without delay; 'timeless'
ehipassiko: inviting inspection
opaneyyiko: leading onwards (to experiencing here-&-now Nibbana)
paccattaṃ veditabbo viññūhī: to be verified by the wise for themselves.
Every morning and every evening, the above verse is chanted by Theravada Buddhists as the recollection of refuge in the Dhamma.
Since the word 'akāliko' is often translated as 'timeless', it appears the word 'akāliko' might be mistaken for 'sanantana' & 'porāṇaka'. However, 'akāliko' means 'immediate' rather than 'eternal'. In short, it appears the Pali word 'akāliko' is not synonymous with 'sanantana' and 'porāṇaka'.