use ‧ ful ‧ ness /ˈjuːsf ə lnəs, ˈjuːsf ə lnɪs/ BrE AmE noun [uncountable]
[ Word Family: noun : ↑ usage , ↑ use , ↑ disuse , ↑ misuse , ↑ reuse , ↑ usefulness ≠ ↑ uselessness , ↑ user ; adjective : ↑ reusable , used ≠ ↑ unused , ↑ disused , ↑ useful ≠ ↑ useless , ↑ usable ≠ ↑ unusable ; verb : ↑ use , ↑ misuse , ↑ reuse ; adverb : ↑ usefully ≠ ↑ uselessly ]
the state of being useful or the degree to which something is useful
usefulness of
There are doubts as to the usefulness of this approach (=it may not be useful) .
As a commuter service, the ferry has outlived its usefulness (=is no longer useful) .