The American Heritage® Dictionary of the English Language, 4th Edition
verb-intransitive. To slip or skid to one side.
verb-intransitive. To slide sideways and downward in skiing.
verb-intransitive. To fly sideways and downward in an airplane along the lateral axis to reduce altitude without gaining speed or as the result of banking too deeply.
Word Usage
"There's probably a lot of short-term sideslip in the twenty-second century, but by the time it reaches us, it all irons out in the wash. ""