Definition of "greuous"

If anie do dislike the superstitious & needles cærimonies in ordination & yet also acknowledg that the Byshops may call, authorise, trie, confirme, & warrant by testimonie the sufficiencie of ministers / what greuous synne is it.

1588?, Robert Browne, “A Reproofe of Certeine Schismatical Persons & Their Doctrine Touching the Hearing & Preaching of the Word of God” in Cartwrightiana, ed. Albert Peel and Leland Henry Carlson (1951, published for the Sir Halley Stewart Trust by Allen and Unwin), page 228