pig vs litterbug

pig and litterbug both are nouns.

Word	Noun	Adjective	Verb	Adverb
pig	Yes	No	Yes	No
litterbug	Yes	No	No	No

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

Other hyponyms of pig include litter lout, litterer, slattern, slovenly woman, slut, trollop.

pig (noun)	litterbug (noun)
domestic swine	a person who litters public places with refuse
a crude block of metal (lead or iron) poured from a smelting furnace
mold consisting of a bed of sand in which pig iron is cast
a person regarded as greedy and pig-like
uncomplimentary terms for a policeman
a coarse obnoxious person