slaves is a form of:

Heavily



adverb
1.
(With a great weight, ponderously, oppressively, arduously, awkwardly, abundantly) walk heavily ជើងធ្ងន់ rain heavily យ៉ាងខ្លាំង, heavily loaded យ៉ាងធ្ងន់ heavily populated ដែលមានប្រជាជនច្រើន
ENGLISH MEANING
adverb
1.
In a heavy manner; with great weight; as, to bear heavily on a thing; to be heavily loaded.
2.
As if burdened with a great weight; slowly and laboriously; with difficulty; hence, in a slow, difficult, or suffering manner; sorrowfully.