Adjective

(en adjective)

Making good, thorough, or careful use of resources; not consuming extra. Especially, making good use of time or energy.

* {{quote-magazine, title=A better waterworks, date=2013-06-01, volume=407, issue=8838

, page=5 (Technology Quarterly), magazine=(The Economist) citation , passage=An artificial kidney these days still means a refrigerator-sized dialysis machine. Such devices mimic

Using a particular proportion of available energy.

Causing effects; producing results.

* Wilson

The efficient cause is the working cause.

Adjective

(en adjective)

Incapable of producing results; useless; not successful; not worth attempting.

*

, title=(The Celebrity), chapter=4 , passage=No matter how early I came down, I would find him on the veranda, smoking cigarettes, or

*

*:There is an hour or two, after the passengers have embarked, which is disquieting and fussy.Stewards, carrying cabin trunks, swarm in the corridors. Passengers wander restlessly about or hurry, with futile energy, from place to place.

*{{quote-news, year=2011, date=December 15, author=Marc Higginson, work=BBC Sport

, title= Shamrock Rovers 0-4 Tottenham , passage=Goals from Steven Pienaar, Andros Townsend, Jermain Defoe and Harry Kane sealed the win, but Rubin Kazan's 1-1 draw against PAOK Salonika rendered Spurs' efforts futile .}}