ploughman's lunch vs meal

ploughman's lunch and meal both are nouns.

Word	Noun	Adjective	Verb	Adverb
ploughman's lunch	Yes	No	No	No
meal	Yes	No	No	No

As nouns, meal is a hypernym of ploughman's lunch; that is, meal is a word with a broader meaning than ploughman's lunch:

ploughman's lunch: a meal consisting of a sandwich of bread and cheese and a salad
meal: the food served and eaten at one time

Other hypernyms of ploughman's lunch include repast.

ploughman's lunch (noun)	meal (noun)
a meal consisting of a sandwich of bread and cheese and a salad	the food served and eaten at one time
	coarsely ground foodstuff; especially seeds of various cereal grasses or pulse
	any of the occasions for eating food that occur by custom or habit at more or less fixed times