Definition of "unassailable"

Yet in the number, I do know but One That vnaſſayleable holds on his Ranke, Vnfhak’d of Motion : and that I am he, Let me a little ſhew it, euen in this : That I was conſtant Cymber ſhould be baniſh’d, And conſtant do remaine to keepe him ſo.

1599 (first performance), William Shakespeare, “The Tragedie of Iulius Cæsar”, in Mr. William Shakespeares Comedies, Histories, & Tragedies […] (First Folio), London: […] Isaac Iaggard, and Ed[ward] Blount, published 1623, [Act III, scene i], page 119, column 1

His recourse to written documents to make his discourse unassailable has created a virtually unalterable situation even as he is on the verge of being forced to “see through” Tartuffe.

1990, Larry W. Riggs, “Moliere’s “Poststructuralism”: Demolition of Transcendentalist Discourse in Le Tartuffe”, in Symposium: A Quarterly Journal in Modern Literatures, volume 44, number 1, page 53

None of the processes, however, is either uniform or unassailable. The contradictions and distortions within any hegemonic discourse, as well as the discrepancies between it and the popular understandings of common sense, leave it ever vulnerable to penetration, criticism, and refusal.

1990, James Brow, “Notes on Community, Hegemony, and the Uses of the Past”, in Anthropological Quarterly, volume 63, number 1, George Washington U Institute for Ethnographic Research, page 5