supper vs Seder

supper and Seder both are nouns.

Word	Noun	Adjective	Verb	Adverb
supper	Yes	No	No	No
Seder	Yes	No	No	No

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

supper: a light evening meal; served in early evening if dinner is at midday or served late in the evening at bedtime
Seder: (Judaism) the ceremonial dinner on the first night (or both nights) of Passover

Other hyponyms of supper include Passover supper.

supper (noun)	Seder (noun)
a light evening meal; served in early evening if dinner is at midday or served late in the evening at bedtime	(Judaism) the ceremonial dinner on the first night (or both nights) of Passover
a social gathering where a light evening meal is served