language unit vs sound

language unit and sound both are nouns.

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

As nouns, sound is a hyponym of language unit; that is, sound is a word with a more specific, narrower meaning than language unit:

language unit: one of the natural units into which linguistic messages can be analyzed
sound: (phonetics) an individual sound unit of speech without concern as to whether or not it is a phoneme of some language

Other hyponyms of language unit include discourse, word, syllable, lexeme, morpheme, formative, name, collocation, phone, speech sound, sign.

language unit (noun)	sound (noun)
one of the natural units into which linguistic messages can be analyzed	the particular auditory effect produced by a given cause
	the subjective sensation of hearing something
	the audible part of a transmitted signal
	(phonetics) an individual sound unit of speech without concern as to whether or not it is a phoneme of some language
	the sudden occurrence of an audible event
	a large ocean inlet or deep bay
	a narrow channel of the sea joining two larger bodies of water
	mechanical vibrations transmitted by an elastic medium

language unit (adjective)	sound (adjective)
	financially secure and safe
	in good condition; free from defect or damage or decay
	complete; thorough
	(of sleep) deep and complete
	in excellent physical condition
	exercising or showing good judgment
	free from moral defect
	vigorous or severe
	having legal efficacy or force
	logically valid

language unit (verb)	sound (verb)
	measure the depth of (a body of water) with a sounding line
	utter with vibrating vocal chords
	make a certain noise or sound
	cause to sound
	announce by means of a sound
	give off a certain sound or sounds
	appear in a certain way