labial vs bilabial

labial and bilabial both are nouns.

Word	Noun	Adjective	Verb	Adverb
labial	Yes	Yes	No	No
bilabial	Yes	Yes	No	No

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

labial: a consonant whose articulation involves movement of the lips
bilabial: a consonant that is articulated using both lips; /p/ or /b/ or /w/

Other hyponyms of labial include labial stop.

labial (noun)	bilabial (noun)
a consonant whose articulation involves movement of the lips	a consonant that is articulated using both lips; /p/ or /b/ or /w/

labial (adjective)	bilabial (adjective)
relating to or near the female labium	of or relating to or being a speech sound that is articulated using both lips
of or relating to the lips of the mouth