baulker

/ˈbɔːkər/
noun
  1. A person or thing that refuses to proceed or act, or that deliberately obstructs progress.
    • The old engine was a baulker and often stalled on cold mornings.
    • The horse was a known baulker and would stop at every fence.
    • In the meeting, he acted as a baulker, blocking every new idea.
Antonyms
What does "baulker" mean? | whatsthatwordmean | whatsthatwordmean