efficient and effective

If somebody/something is efficient, he/she/it works in a well-organised way without wasting time or energy.

• He’s not very efficient: he works very slowly, and he keeps forgetting things.
• Our bus service is even less efficient than our train service.

If something is effective, it has the right effect: it solves a problem or gets a result.

• My headache’s much better. Those tablets really are effective.
• I think a wide black belt would look very effective with that dress.