I'm just curious if the word "holiday" is derived from "holy day".
That's right. According to Etymonline:
O.E. haligdæg, from halig "holy" + dæg "day;" in 14c. meaning both "religious festival" and "day of recreation", but pronunciation and sense diverged 16c.
The answers are above, but Barnhart's Dictionary of Etymology offers a bit more:
Old English had a concurrent open compound halig daeg, found later in Middle English holy day, which became modern English holiday, meaning both a religious festival and a day of recreation. This eventually replaced the earlier form haliday, leaving two forms holiday and holy day.
Holiday is a compound stemming from the words holy and day. The word 'holiday' first surfaced in the 1500's replacing the earlier word 'haliday' which was recorded before 1200 in the Old English book Ancrene Riwle. Earlier , about 950, the word was 'haligdaeg' and appeared in the Old English Lindisfarne Gospels. It was a compound of halig (holy) plus daeg (day)