• usefull

From use +‎ -ful.

• (Received Pronunciation) IPA^(key): /ˈjuːsfl̩/, [ˈjuːsfɫ̩]
• (General American, Canada) IPA^(key): /ˈjusfl̩/, [ˈjusfɫ̩]

  • Audio (California):

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• (General Australian, New Zealand) IPA^(key): /ˈjʉːsfəl/, [ˈjʉːsfɫ̩]

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

1. Having a practical or beneficial use.

   Synonyms: noteful, salutary, serviceable, utilitarian, utile, purposive

   Antonyms: unuseful, useless, unusable, unutilizable, inutile (obsolete)

   prove useful

   practically useful

   That’s a very useful tool for gardeners.

   She found the information extremely useful.

   • 1960 December, Cecil J. Allen, “Operating a mountain main line: the Bern-Lötschberg-Simplon: Part One”, in Trains Illustrated, page 743:

     In the early days troubles were experienced with oscillation from the rod drive and with the transformers, but were overcome later, and these machines performed useful service until superseded by more modern locomotives less costly in maintenance.

   • 2013 July–August, Lee S. Langston, “The Adaptable Gas Turbine”, in American Scientist:

     Turbines have been around for a long time—windmills and water wheels are early examples. The name comes from the Latin turbo, meaning vortex, and thus the defining property of a turbine is that a fluid or gas turns the blades of a rotor, which is attached to a shaft that can perform useful work.

• 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.