The Collaborative International Dictionary of English v.0.48:

Downtrod \Down"trod`\, Downtrodden \Down"trod`den\, a.
   Trodden down; trampled down; abused by superior power.
   --Shak. Downward

WordNet (r) 3.0 (2006):

downtrodden
    adj 1: abused or oppressed by people in power

Moby Thesaurus II by Grady Ward, 1.0:

31 Moby Thesaurus words for "downtrodden":
   abject, abused, afflicted, beat, beaten, browbeaten, burdened,
   cowed, downtrod, ground down, henpecked, in leading strings,
   maltreated, mistreated, misused, oppressed, ordered around,
   overborne, overcome, overwhelmed, persecuted, plagued, regimented,
   servile, slavish, subjugated, submissive, trampled, tyrannized,
   underfoot, unmanned