syllable vs language unit

syllable and language unit both are nouns.

Word	Noun	Adjective	Verb	Adverb
syllable	Yes	No	No	No
language unit	Yes	No	No	No

As nouns, language unit is a hypernym of syllable; that is, language unit is a word with a broader meaning than syllable:

syllable: a unit of spoken language larger than a phoneme
language unit: one of the natural units into which linguistic messages can be analyzed

Other hypernyms of syllable include linguistic unit.

syllable (noun)	language unit (noun)
a unit of spoken language larger than a phoneme	one of the natural units into which linguistic messages can be analyzed