causing effects, producing results; bringing into being; initiating change (rare except in philosophical and legal expression efficient cause = causative factor or agent)
expressing the proportion of consumed energy that was successfully used in a process; the ratio of useful output to total input
making good, thorough, or careful use of resources; not consuming extra. Especially, making good use of time or energy
effective, efficacious
Inconstant in purpose, or volatile in behavior.
Lacking regularity or uniformity.
Not held firmly in position, physically unstable.
To render unsteady, removing balance.