(Australia, New Zealand, Britain, Ireland) A hand tool for adjusting nuts and bolts; a wrench.

(rare) One who, or that which, spans.

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

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

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

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

To use a spanner; to fix with a spanner