from The American Heritage® Dictionary of the English Language, 4th Edition
- adj. Not remissible; unpardonable: irremissible sins.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- adj. Not remissible.
from the GNU version of the Collaborative International Dictionary of English
- adj. Not remissible; unpardonable.
from The Century Dictionary and Cyclopedia
- Not remissible; not capable of being remitted; unpardonable: as, an irremissible sin.
True it is that in writing of the extent of the power conferred, he makes exception for the sins of idolatry and adultery, which he terms irremissible, although Dionysius of Corinth (170) years before held that no sin was excepted from the power of the keys granted by Christ to His Church (Eusebius, Hist.
Thus Tertullian admits the power of the bishop for all but "irremissible" sins.
That then that is said, "All manner of sin and blasphemy shall be forgiven unto men," without doubt blasphemy spoken against the Father is included in its largeness; though here again that alone is declared irremissible which is spoken against the Holy Ghost.
"irremissible," not in the same manner as that in which unbelief and final impenitence are unpardonable, through this decree of God: "He that believeth not on the Son of God, is condemned," and "Unless ye repent and be converted, ye shall all likewise perish," &c.
Theodorus Bibliander, &c. Many foolish ceremonies you shall find in them; and which is most to be lamented, the people are generally so curious in observing of them, that if the least circumstance be omitted, they think they shall be damned, 'tis an irremissible offence, and can hardly be forgiven.
Making idiotic excuses for her irremissible behavior is far worse:
Sinning, therefore, in all these particulars, against the Spirit of God,  they fall into the irremissible sin.
Besides, the cause why that sin is irremissible, unto death, and why the man who thus sins cannot be renewed unto repentance, seems to be rendered in Hebrews 6, in the following terms: "- seeing they crucify to themselves the Son of God afresh, and put him to an open shame."
From these remarks, I think, we may easily solve the difficulty which lies in the words of Christ, who distinguishes this "sin against the Holy Ghost" from "the sin against the Son of Man," and who declares that the former is irremissible or unpardonable, but that the latter is capable of forgiveness.
We have now arrived at the seventh division, which relates to the adjunct or attribute peculiar to this sin, that is, its being irremissible or unpardonable, and the cause why it is thus incapable of being forgiven.