Old English vs Anglian

Old English and Anglian both are nouns.

Word	Noun	Adjective	Verb	Adverb
Old English	Yes	No	No	No
Anglian	Yes	No	No	No

As nouns, Anglian is a hyponym of Old English; that is, Anglian is a word with a more specific, narrower meaning than Old English:

Old English: English prior to about 1100
Anglian: comprises the Mercian and Northumbrian dialects, two of the major dialects of Old English often classified together as the Anglian dialects

Other hyponyms of Old English include West Saxon, Jutish, Kentish.

Old English (noun)	Anglian (noun)
English prior to about 1100	comprises the Mercian and Northumbrian dialects, two of the major dialects of Old English often classified together as the Anglian dialects