成唯識論演祕 1.171

1.171

釋第五解為重之義。有義：對業果故，貪等自性能引業果，眾苦本故，故名為重。

This explains the meaning of 'grave' in the fifth interpretation. There is an opinion: because they correspond to karma and its fruit, the intrinsic nature of greed and the like can induce karma and its fruit, and being the root of many sufferings, they are therefore called 'grave'.