The Collaborative International Dictionary of English v.0.48:

Pinkster \Pink"ster\, n. [D. pinkster, pinksteren, fr. Gr. ?.
   See Pentecost.]
   Whitsuntide. [Written also pingster and pinxter.]
   [1913 Webster]

   Pinkster flower (Bot.), the rosy flower of the Azalea
      nudiflora; also, the shrub itself; -- called also
      Pinxter blomachee by the New York descendants of the
      Dutch settlers.
      [1913 Webster]