What might break Mavericks "look up" gesture?

On my main OSX account, the define gesture on my trackpad (three finger gap) recently stopped working. It's checked in System Preferences, but not functioning. This affects both my magic trackpad and my MacBook's built in trackpad.

So far, I've tried:

• Deleted com.apple.AppleMultitouchTrackpad.plist and com.apple.driver.AppleBluetoothMultitouch.trackpad.plist.
• Deleted and re-paired the trackpad.

This isn't a hardware issue, as an another user account on the same computer works fine.

Has anyone seen this? What might be wrong?

Although I never found which preference file was responsible, deleting all of them (I'd already tried com.apple.AppleMultitouchTrackpad.plist and com.apple.driver.AppleBluetoothMultitouch.trackpad.plist) restored the gesture.