drop out vs dropout vs drop-out [closed]

Dictionaries generally agree that drop out is the verb form and dropout or drop-out is the noun form. (See Merriam-Webster, which has dropout for the noun, and the Oxford English Dictionary, which has drop-out for the noun.) This fits a general pattern for nouns formed from phrasal verbs: as a noun they tend to form a word without a space or a hyphenated word:

go-ahead, breakdown, mix-up

The same ambiguity persists for the adjective. Collins Dictionary lists dropout as an adjective and noun form, noting "also drop-out." So both forms are used for nouns and adjectives.

If you go by frequency, dropout is about ten times more frequent in the Corpus of Contemporary American English than drop-out (around 2600 compared to around 250). The Ngram search is flawed with hyphenation but generates a similar result.

One final factor is that compound adjectives that express a single idea are often hyphenated. So if you wanted to conform to this rule, the adjective form would be drop-out.

So it's your decision how you use the noun and adjective forms. You can technically use dropout for both, use drop-out to distinguish the adjective from the noun, or even go against common usage and use drop-out for both. You make the call.