article vs knickknack

article and knickknack both are nouns.

Word	Noun	Adjective	Verb	Adverb
article	Yes	No	Yes	No
knickknack	Yes	No	No	No

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

Other hyponyms of article include breakable, novelty, notion, ware.

article (noun)	knickknack (noun)
one of a class of artifacts	miscellaneous curios
nonfictional prose forming an independent part of a publication	a small inexpensive mass-produced article
(grammar) a determiner that may indicate the specificity of reference of a noun phrase
a separate section of a legal document (as a statute or contract or will)

article (verb)	knickknack (verb)
bind by a contract; especially for a training period