combining vs attachment

combining and attachment both are nouns.

Word	Noun	Adjective	Verb	Adverb
combining	Yes	No	No	No
attachment	Yes	No	No	No

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

combining (noun)	attachment (noun)
the act of combining things to form a new whole	the act of fastening things together
an occurrence that results in things being united	the act of attaching or affixing something
	faithful support for a cause or political party or religion
	a supplementary part or accessory
	a connection that fastens things together
	a writ authorizing the seizure of property that may be needed for the payment of a judgment in a judicial proceeding
	a feeling of affection for a person or an institution