Real Dictionary

tune up
phrasal verb: When a group of musicians tune up, they adjust their instruments so that they produce the right notes.

tune up in American English
to adjust (musical instruments) to the same pitch, as in an orchestra
to cause a group of musical instruments to be brought to the same pitch

tune up in British English
to adjust (a musical instrument) to a particular pitch, esp a standard one
noun: adjustments made to an engine to improve its performance

tune-up in American English
noun: an adjustment, as of a motor, to improve working order or condition

tune-up in British English
noun: a regular maintenance or service performed on a car or other automobile