abandon vs fall in

abandon is a noun but fall in is not a noun.

Word	Noun	Adjective	Verb	Adverb
abandon	Yes	No	Yes	No
fall in	No	No	Yes	No

abandon (noun)	fall in (noun)
the trait of lacking restraint or control; reckless freedom from inhibition or worry
a feeling of extreme emotional intensity

abandon (verb)	fall in (verb)
leave someone who needs or counts on you; leave in the lurch	break down, literally or metaphorically
stop maintaining or insisting on; of ideas or claims	become part of; become a member of a group or organization
leave behind empty; move out of	to take one's place in a military formation or line
forsake, leave behind
give up with the intent of never claiming again