efficient

noun

A cause; something that causes an effect

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

   An efficient process would automate all the routine work.

2. Expressing the proportion of consumed energy that was successfully used in a process; the ratio of useful output to total input

   The motor is only 20% efficient at that temperature.

3. Causing effects, producing results; bringing into being; initiating change (rare except in philosophical and legal expression efficient cause = causative factor or agent)

   Ownership, maintenance, or use of the automobile need not be the direct and efficient cause of the injury sustained

4. (old use) effective