Proficuous: useful or profitable.

But how to use?

Cash proved proficuous for/in/at securing the deal.

  • 3
    Don't use it. Merriam-Webster is one of the few dictionaries to list it, as obsolete. Commented Apr 28 at 18:50
  • It is a rare word in English, definitely outdated: see here books.google.com/ngrams/…
    – user 66974
    Commented Apr 28 at 18:54
  • Perhaps "essential for securing the deal" might work in the example context. Or "essential to secure the deal". Commented Apr 28 at 18:59
  • It's likely to be confused or misread for other more common words (proficient, profit-something, prosperous, promiscuous, profuse, etc) with unpredictable effects.
    – Stuart F
    Commented Apr 29 at 10:15

1 Answer 1


OED lists three prepositions, among other usages:

1665 You may now believe nothing more proficuous against the Plague..than Phlebotomy. — G. Harvey, Discourse of Plague xviii. 28

1788 An immense sum..which, if employed in encouraging the manufacture of..the natural products of the country, would certainly have been more proficuous to the public weal.
— T. Denham, Temporal Government of Pope's State xxv. 237

1992 Today, it has found a more proficuous application in expanding cable program capacity.
Video Age International (Nexis) April 64

If you are going to use it, then use whatever preposition seems best in the circumstances. OED indicates that useful is a direct equivalent. Substitute useful if you're in doubt and see which preposition fits best: use that one.

However, even though OED has found a citation from as recent as 1992, it also says that the word has a frequency of fewer than 0.01 occurrences per million in modern English usage. That is, perficuous would, on average, appear once in 100 million words — about 125 complete bibles, or 2½ Encyclopaedia Britannicas.

Using proficuous is not a good idea. Useful is likely to be more proficuous.

  • 1
    I admire the proficuity of this answer.
    – Sven Yargs
    Commented Apr 29 at 5:50

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