Sentence:  Working a 12:30 pm. to 9:00 pm. work shift raises the question: How can you tell the difference between the meals “linner” and “<WSD>lupper</WSD>?” Well, “linner” is closer to the normal lunch hour, and “lupper” is closer to supper. 
Meaning of the word marked with <WSD> tags:  A meal or snack eaten between the normal times for lunch and supper.