different between useful vs unreleased

English

From use +? -ful.

useful (comparative usefuller or more useful, superlative usefullest or most useful)

Having a practical or beneficial use.
Synonyms: noteful, serviceable, utilitarian, utile
Antonyms: unuseful, useless, harmful

Prepositions: useful is used in useful for <purpose>, useful for <person> and useful to <person>. The words useful to are also found in constructions such as It is useful to do, in which to marks an infinitive rather than being a preposition.

un- +? released

unreleased (not comparable)

Not released.
Fans were soon sharing the band's unreleased songs on the Internet.
(linguistics, phonology) Of a stop consonant, remaining occluded when spoken.

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