INEXCUSABLY

unjustifiably, inexcusably

(adverb) without any excuse; “he is unjustifiably harsh on her”

inexcusably, unpardonably, unforgivably

(adverb) in an unpardonable manner or to an unpardonable degree; “he was inexcusably cruel to his wife”

Source: WordNet® 3.1

Etymology

Adverb

inexcusably (comparative more inexcusably, superlative most inexcusably)

In an inexcusable manner.

Source: Wiktionary

In`ex*cus"a*bly, adv.

Definition: With a degree of guilt or folly beyond excuse or justification. Inexcusably obstinate and perverse. Jortin.

INEXCUSABLE

In`ex*cus"a*ble, a. Etym: [L. inexcusabilis: cf. F. inexcusable. See Excuse.]

Definition: Not excusable; not admitting excuse or justification; as, inexcusable folly. Therefore thou art inexcusable, O man, whosoever thou art that judgest; for wherein thou judgest another, thou condemnest thyself; for thou that judgest doest the same things. Rom. ii. 1.

Source: Webster’s Unabridged Dictionary 1913 Edition