skink vs mountain skink

skink and mountain skink both are nouns.

Word	Noun	Adjective	Verb	Adverb
skink	Yes	No	No	No
mountain skink	Yes	No	No	No

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

skink: alert agile lizard with reduced limbs and an elongated body covered with shiny scales; more dependent on moisture than most lizards; found in tropical regions worldwide
mountain skink: frequents oak and pine habitats in rocky mountainous areas of United States southwest and Mexico

Other hyponyms of skink include Eumeces skiltonianus, western skink, Eumeces callicephalus.

skink (noun)	mountain skink (noun)
alert agile lizard with reduced limbs and an elongated body covered with shiny scales; more dependent on moisture than most lizards; found in tropical regions worldwide	frequents oak and pine habitats in rocky mountainous areas of United States southwest and Mexico