Meaning

• A hand tool for adjusting nuts and bolts; a wrench.

  "Pass me that spanner, Jake; there's just one more nut to screw in."

• One who, or that which, spans.

• A hand tool shaped like a small crank handle, for winding the spring of a wheel lock on a musket.

• A device in early steam engines for moving the valves for the alternate admission and shutting off of the steam.

• A problem, dilemma or obstacle; something unexpected or troublesome (in the phrase spanner in the works)

• (mildly) A stupid or unintelligent person; one prone to making mistakes, especially in language.