meal vs tiffin

meal and tiffin both are nouns.

Word	Noun	Adjective	Verb	Adverb
meal	Yes	No	No	No
tiffin	Yes	No	No	No

As nouns, tiffin is a hyponym of meal; that is, tiffin is a word with a more specific, narrower meaning than meal:

meal (noun)	tiffin (noun)
the food served and eaten at one time	a midday meal
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