Verb, participle, perfect, passive, dative masculine, plural.
Participles are verbal adjectives; in this case the participle is used as a substitute for the Corinthians Christians whom Paul sees as 'sanctified' and being so. The English word 'saint' used in the NIV is a less literal translation but is not inappropriate since it is derived from the same root.
Open Alberith Greek Wordbook on hagios
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