formation vs flank

formation and flank both are nouns.

Word	Noun	Adjective	Verb	Adverb
formation	Yes	No	No	No
flank	Yes	No	Yes	No

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

Other hyponyms of formation include flight, military formation, backfield, secondary, line, line, center, centre, wing, head, rear.

formation (noun)	flank (noun)
the act of fabricating something in a particular shape	the side between ribs and hipbone
the act of forming or establishing something	a cut from the fleshy part of an animal's side between the ribs and the leg
creation by mental activity	the side of military or naval formation
a particular spatial arrangement	a subfigure consisting of a side of something
an arrangement of people or things acting as a unit
(geology) the geological features of the earth
natural process that causes something to form

formation (verb)	flank (verb)
	be located at the sides of something or somebody