the GNU version of the Collaborative International Dictionary of English
preposition. Whether one or another; whether one or the other; which; that one (of two or more) which.
The Century Dictionary and Cyclopedia
Whether one or the other; no matter which.
Word Usage
"This guidance does not apply to health care settings where the exclusion period should be continued for 7 days from symptom onset or until the resolution of symptoms, whichever is longer."