Both ἅγιος (connected with ἁγνός, ’pure’) and ὅσιος are translated ’holy,’ and both are employed in reference to the Lord as "the holy One," [Mar 1:24] (ἅγ.) and [Act 2:27] and [Act 13:35] (ὅσ.).
There are two corresponding words in the Hebrew, and both occur in Psa 89: ὅσιος corresponds with chasid, "thy holy One," [Psa 89:19]; and ἅγιος with qadôsh, "the holy One" in [Psa 89:18], the singular of the word translated ’saints’ in [Psa 89:5]; [Psa 89:7]. ὅσιος, in the neuter plural, is rendered ’mercies’ in "the sure mercies of David" in [Act 13:34]
The difference of the two words has been well expressed thus: God is holy, knowing good and evil perfectly - wills absolutely good and no evil: and we are separated, set apart from evil or common use to Him that is ἅγιος. ὅσιος, on the contrary, is the exercise of gracious suitable affections in the relationships in which we stand to God, to parents, etc.; also God in mercy to us, and Christ in whom they are displayed. Hence however, as suitable affections towards God practically constitute holiness, it is used in this sense for holiness. Its only occurrences are [Act 2:27]; [Act 13:34-35]; [1Ti 2:8]; [Tit 1:8]; [Heb 7:26]; [Rev 15:4]; [Rev 16:5]. Thus it is, as is its Hebrew equivalent, employed of God and man. It is goodness and grace in God - piety and recognition of Him on man’s part, and is so used of Christ as the One in whom all gracious qualities are concentrated
ἅγιος is of much more frequent use.
