The Collaborative International Dictionary of English v.0.48:

Stagnate \Stag"nate\ (st[a^]g"n[=a]t), v. i. [imp. & p. p.
   Stagnated (-n[asl]*t[e^]d); p. pr. & vb. n. Stagnating.]
   [L. stagnatus, p. p. of stagnare to stagnate, make stagnant,
   from stagnum a piece of standing water. See Stank a pool,
   and cf. Stanch, v. t.]
   1. To cease to flow; to be motionless; as, blood stagnates in
      the veins of an animal; hence, to become impure or foul by
      want of motion; as, air stagnates in a close room.
      [1913 Webster]

   2. To cease to be brisk or active; to become dull or
      inactive; as, commerce stagnates; business stagnates.
      [1913 Webster]

            Ready-witted tenderness . . . never stagnates in
            vain lamentations while there is any room for hope.
                                                  --Sir W.
                                                  Scott.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Stagnate \Stag"nate\ (-n[asl]t), a.
   Stagnant. [Obs.] "A stagnate mass of vapors." --Young.
   [1913 Webster]

WordNet (r) 3.0 (2006):

stagnate
    v 1: stand still; "Industry will stagnate if we do not stimulate
         our economy"
    2: cause to stagnate; "There are marshes that stagnate the
       waters"
    3: cease to flow; stand without moving; "Stagnating waters";
       "blood stagnates in the capillaries"
    4: be idle; exist in a changeless situation; "The old man sat
       and stagnated on his porch"; "He slugged in bed all morning"
       [syn: idle, laze, slug, stagnate] [ant: work]

Moby Thesaurus II by Grady Ward, 1.0:

40 Moby Thesaurus words for "stagnate":
   be a sideliner, be still, coast, constipate, decay, decline,
   decompose, degenerate, delay, deteriorate, do nothing, drift, fust,
   go to pot, go to seed, hang fire, hibernate, idle, just be,
   languish, lie dormant, merely exist, moulder, not budge, not stir,
   pass the time, rest, rot, rust, sit back, sit it out, sleep,
   slumber, smolder, spoil, stifle, trammel, vegetate, wait and see,
   watch and wait