Sure it is, in a number of places. For example, your buddy +Paul uses it in Ephesians referring to the Mysterion of Marriage. You'll find several in Corinthians. One of the best descriptions of Apostles/bishops/priests is at 1 Cor. 4:1 "...οἰκονόμους μυστηρίων θεοῦ", "stewards of the mysteries of God". The Greek is beautiful, bb! And there are more examples. You may want to learn Greek for your bible studying. English will lead you wrong as often as not.
As they say—amen to that.
I'm sure Greek IS a beautiful language and Hebrew as well. I appreciate the wonderful study guides, concordances and lexicons we have today so that every single word in the Bible can be looked up and the word in the original language is given along with the meaning and other uses of it.
It is curious that the word "sacrament" is not used anywhere in the English language translations but, as you said the word means mystery. I wonder why then that it did not get translated that way? There are many places where the word IS translated as mystery from the Greek "mysterion" and according to the Strong's concordance, it means a hidden thing or secret. It even has that meaning in the Hebrew OT.
So I'm not getting the sense that it is really like you say in that it implies the same thing as the Church's term "sacrament". For example, there is the "mystery of the Kingdom"; the mystery of Israel's salvation; the mystery of the Gospel being preached to all the world; the mystery of the hidden wisdom of God; the mystery that we will not all die but we will all be changed; the mystery of Christ in us; mystery of faith; mystery of Godliness; even a mystery of the seven stars and the mystery of iniquity and, finally, the mystery of the whore of Babylon. But I did not find anywhere a mystery of marriage, of baptism, of communion/Eucharist, of Holy Orders, of healing or of last rites that would justify your assertion of the sacraments being described in Scripture.
I'm fully aware that the Church developed these doctrines of the seven sacraments, but they were really not spelled out as such in Scripture.