The Collaborative International Dictionary of English v.0.48:

Dicentra \Di*cen"tra\ (d[-i]*s[e^]n"tr[.a]), Prop. n. [NL., fr.
   Gr. di- = di`s- twice + ke`ntron spur.] (Bot.)
   A genus of herbaceous plants, with racemes of two-spurred or
   heart-shaped flowers, including the Dutchman's breeches,
   and the more showy Bleeding heart (Dicentra spectabilis).
   [Corruptly written dielytra.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

bleeding heart
    n 1: garden plant having deep-pink drooping heart-shaped flowers
         [syn: bleeding heart, lyreflower, lyre-flower,
         Dicentra spectabilis]
    2: someone who is excessively sympathetic toward those who claim
       to be exploited or underprivileged

Moby Thesaurus II by Grady Ward, 1.0:

64 Moby Thesaurus words for "bleeding heart":
   aching heart, agony, agony of mind, anguish, bale, bathos,
   bitterness, bowels of compassion, broken heart, brokenheartedness,
   cloyingness, compassionateness, crushing, depression,
   depth of misery, desolation, despair, extremity, gentleness, goo,
   grief, heartache, heartbreak, heartbrokenness, hearts-and-flowers,
   heartsickness, heartsoreness, heavy heart, infelicity, lenity,
   maudlinness, mawkishness, melancholia, melancholy, mercifulness,
   misery, mush, mushiness, namby-pamby, namby-pambyism,
   namby-pambyness, nostalgia, nostomania, oversentimentalism,
   oversentimentality, prostration, romanticism, ruthfulness, sadness,
   sentiment, sentimentalism, sentimentality, slop, sloppiness, slush,
   soap opera, sob story, softheartedness, suicidal despair,
   sweetness and light, tearjerker, tenderness, woe, wretchedness