The Collaborative International Dictionary of English v.0.48:

Unblenching \Unblenching\
   See blenching.

Moby Thesaurus II by Grady Ward, 1.0:

39 Moby Thesaurus words for "unblenching":
   audacious, bold, calm, coolheaded, courageous, dauntless, fearless,
   inexcitable, intrepid, nerveless, relaxed, rock-steady, steady,
   steady-handed, steady-nerved, steel-nerved, strong-nerved,
   unabashed, unappalled, unawed, unblinking, uncowed, uncringing,
   undaunted, undismayed, unfaltering, unflinching, unintimidated,
   unnervous, unquivering, unshaken, unshaky, unshrinking, unstrained,
   untremulous, unwavering, valiant, valorous, without a tremor