effective, efficacious
expressing the proportion of consumed energy that was successfully used in a process; the ratio of useful output to total input
causing effects, producing results; bringing into being; initiating change (rare except in philosophical and legal expression efficient cause = causative factor or agent)
making good, thorough, or careful use of resources; not consuming extra. Especially, making good use of time or energy
Thieving, thievish.
Used other than figuratively or idiomatically: see nimble, fingered.