Putting the dog in the dishwasher may be an effective cleaning solution, but hardly efficient (as the dog would probably die).

Putting the dog in the dishwasher may be an effective cleaning solution, but hardly efficient (as the dog would probably die). Photo copyright Malcolm Pemberton 2012.

Here are two more words that are often used wrongly.

To be efficient is to make good use of your time and available resources, so that the job gets done well with the minimum of waste. Being efficient usually involves looking at the bigger picture too. Efficient is often used with other words to create compound adjectives like fuel-efficient and energy-efficient.
An efficient car carries its occupants in appropriate safety and comfort, whilst using as little energy as practical. Energy-saving lamps are indeed energy-efficient solutions, although perhaps not very cost-effective for the consumer due to a higher purchase price.

The inner components of an energy-efficient bulb. But with all these components, and the mercury in the tube, to be disposed of, perhaps the bulbs are not so efficient overall.

The inner components of an energy-efficient bulb. But with all these components, and the mercury in the tube to be disposed of, perhaps the bulbs are not so efficient overall. Photo copyright Malcolm Pemberton 2012.

To be effective simply means that the job gets done well.Pouring petrol on an ants’ nest and setting fire to it is an effective way of getting rid of the ants, but there may be unwanted side-effects. A cost-effective solution concentrates on … well … costs, but may ignore, for example, aspects of quality. Jogging is an effective form of aerobic exercise, it really gets the heart pumping. On the other hand, armchair sport is an effective way of relaxing.