1. n. (Australian, NZ, British, Irish) A hand tool for adjusting nuts and bolts; a wrench.
Pass me that spanner, Jake; there's just one more nut to screw in.
2. n. (rare) One who, or that which, spans.
3. n. (weaponry) A hand tool shaped like a small crank handle, for winding the spring of a wheel lock on a musket.
* 1786, Fig. 10. The spanner for spanning or winding up the spring of the wheel lock. — Francis Grose, A Treatise on Ancient Armour and Weapons, page xvi.
4. n. (obsolete) A device in early steam engines for moving the valves for the alternate admission and shutting off of the steam.
5. n. (UK) A problem, dilemma or obstacle; something unexpected or troublesome (in the phrase spanner in the works)
Halfway through the production of Macbeth, the director found that the stage was smaller than he expected. This really threw a spanner in the works.
6. n. (UK, Irish, mildly, derogatory) A stupid or unintelligent person; one prone to making mistakes, especially in language.
You spanner, Rodney! I wanted a Chinese, not an Indian!