The Collaborative International Dictionary of English v.0.48:

Plodding \Plod"ding\, a.
   Progressing in a slow, toilsome manner; characterized by
   laborious diligence; as, a plodding peddler; a plodding
   student; a man of plodding habits. --Plod"ding*ly, adv.
   [1913 Webster]

WordNet (r) 3.0 (2006):

ploddingly
    adv 1: in a plodding manner; "this writer ploddingly accumulates
           detail after detail"