毫无疑义 is recorded in Liu E's late-Qing novel 《
老残游记》(The Travels of Lao Can, ch. 16).
毫 means 'a fine hair' (i.e. the smallest amount), so the literal sense is 'not a hair's breadth of doubtful meaning' — i.e. completely settled. Synonym:
毫无疑问 háowúyíwèn ('without any doubt').
