The Collaborative International Dictionary of English v.0.48:

lumpen \lump"en\ adj.
   1. mentally sluggish.

   Syn: lumpish, sluggish, unthinking.
        [WordNet 1.5]

The Collaborative International Dictionary of English v.0.48:

Lumpen \Lump"en\, n.
   1. (Politics) same as lumpenproletariat.
      [PJC]

   2. (Zool.) The European eelpout; -- called also lumper.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Lumper \Lump"er\, n. [Cf. Lamper eel.] (Zool.)
   The European eelpout; -- called also lumpen.
   [1913 Webster]

WordNet (r) 3.0 (2006):

lumpen
    adj 1: mentally sluggish [syn: lumpish, lumpen,
           unthinking]