back door vs backdoor

back door and backdoor both are nouns.

Word	Noun	Adjective	Verb	Adverb
back door	Yes	No	No	No
backdoor	Yes	No	No	No

As nouns, back door and backdoor are synonyms defined as:

back door and backdoor: a secret or underhand means of access (to a place or a position)

As nouns, back door and backdoor are synonyms defined as:

Other synonyms of back door include back entrance.

As nouns, back door and backdoor are synonyms defined as:

back door and backdoor: an undocumented way to get access to a computer system or the data it contains

back door (noun)	backdoor (noun)
a secret or underhand means of access (to a place or a position)	a secret or underhand means of access (to a place or a position)
an entrance at the rear of a building	an entrance at the rear of a building
an undocumented way to get access to a computer system or the data it contains	an undocumented way to get access to a computer system or the data it contains