What is the meaning of Heinous?

Totally reprehensible.

Bad, evil or villainous.

Dobson, E[ric] J. (1957), English pronunciation 1500-1700, second edition, volume II: Phonology, Oxford: Clarendon Press, published 1968, →OCLC, § 131 (b), page 650.

Jordan, Richard (1974),  Eugene Crook, transl., Handbook of the Middle English Grammar: Phonology (Janua Linguarum. Series Practica; 218), The Hague: Mouton & Co. N.V., →DOI, § 233, page 213.

Luick, Karl (1929-1940), Herbert Wild, Friedrich Koziol, editors, Historische Grammatik der englischen Sprache, Erster Band, II. Abteilung, Leipzig: Bernhard Tauchnitz, published 1940, →OCLC, § 516, page 634.

Source: wiktionary.org