The Collaborative International Dictionary of English v.0.48:

Plangent \Plan"gent\, a. [L. plangens, -entis, fr. plangere to
   beat. See Plaint.]
   Beating; dashing, as a wave. [R.] "The plangent wave." --H.
   Taylor.
   [1913 Webster] Plani

WordNet (r) 3.0 (2006):

plangent
    adj 1: loud and resounding; "plangent bells"; "the plangent
           minority"

Moby Thesaurus II by Grady Ward, 1.0:

75 Moby Thesaurus words for "plangent":
   Jeremianic, aggrieved, anguished, booming, careworn, complaining,
   consonant, deafening, doleful, dolorous, dumb with grief,
   ear-piercing, ear-rending, ear-splitting, earthshaking,
   faultfinding, forte, fortissimo, fretful, full, grief-stricken,
   griefful, grieved, grievous, howling, in grief, lamentable,
   lamentive, loud, loud-sounding, loudish, lugubrious, mellow,
   moanful, mournful, orotund, pealing, peevish, petulant, piercing,
   plaintive, plunged in grief, puling, pulsing, querulous, resonant,
   resonating, resounding, rich, ringing, rolling, rotund, round,
   rueful, sonorous, sorrowed, sorrowful, sorrowing, stentoraphonic,
   stentorian, stentorious, tearful, throbbing, thunderous,
   tonitruant, tonitruous, ululant, vibrant, vibrating, wailful,
   whimpering, whining, whiny, window-rattling, woeful