Definition of "greevous"

If any therefore demand, which is now most perfection, to ease an extremity by divorce, or to enrage and fester it by the greevous observance of a miserable wedloc, I am not destitute to say which is most perfection (although som who beleev they thinke favourably of divorce, esteem it only venial to informity)

1645, John Milton, Tetrachordon