Originally the Saturday between the traditional Good Friday and Easter was called "Great Sabbath".
It was called that way at least since Chrysostom's time (circa AD 400) according to this reference.
“But when at length he [Polycarp] had brought his prayer to an end, after remembering all that had ever come into contact with him, small and great, famous and obscure, and the whole catholic Church throughout the world, the hour of departure being come, they put him upon an ass and brought him to the city, it being a great Sabbath.1142
[FOOTNOTE]**1142 Σαββ€του μεγ€λου. **“The great Sabbath” in the Christian Church, at least from the time of Chrysostom on, was the Saturday between Good-Friday and Easter. But so far as we know, there are no examples of that use of the phrase earlier than Chrysostom’s time. Lightfoot points out that, in the present instance, it is not “The great Sabbath” (τὸ μέγα Σ€ββατον), but only “A great Sabbath”; and therefore, in the present instance, any great Sabbath might be meant,—that is, any Sabbath which coincided with a festival or other marked day in the Jewish calendar. Lightfoot gives strong reasons for assuming that the traditional day of Polycarp’s death (Feb. 23) is correct, and that the Sabbath referred to here was a great Sabbath because it coincided with the Feast of Purim (see Lightfoot, ibid. I. p. 660 sqq. and 690 sqq.).
And then we see it in this Canon from the Trullo Council in 692 (bold mine)
The faithful spending the days of the Salutatory Passion in fasting, praying and compunction of heart, ought to fast until the midnight of the Great Sabbath: since the divine Evangelists, Matthew and Luke, have shewn us how late at night it was [that the resurrection took place], the one by using the words ὀΨὲ σαββάτων, and the other by the words ὄρθρου βαθέος.
Ancient Epitome of Canon LXXXIX.
On the Great Sabbath the fast must be continued until midnight.
Apparently it was Bede (circa AD 700) and Aquinas (circa AD 1250) who influenced the redefinition of "Great Sabbath" to it's current usage as "Holy Saturday".Not all agreed with that redefinition.
he [the king] was baptized on the Holy Saturday before Easter Day,
And in like manner it is celebrated on Holy Saturday towards the beginning of the night, since our Lord rose in the night, that is, "when it was yet dark, before the sun's rising was manifest."