The most common and most likely answer to this crossword clue is the 7 letter word WORKING
I've seen this crossword clue in Financial Times
W
O
R
K
I
N
G
Buddy explains!
The straight part
We know that "effectiv" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case effectiv = working.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does WORKING mean?
WORKING noun- (usually in the plural) Operation; action.
- Method of operation.
- The incidental or subsidiary calculations performed in solving an overall problem.
- Fermentation.
- (of bodies of water) Becoming full of a vegetable substance.
- A place where work is carried on.
- To do a specific task by employing physical or mental powers.
- To effect by gradual degrees.
- To embroider with thread.
- To set into action.
- To cause to ferment.
- To ferment.
- To exhaust, by working.
- To shape, form, or improve a material.
- To operate in a certain place, area, or speciality.
- To operate in or through; as, to work the phones.
- To provoke or excite; to influence.
- To use or manipulate to one’s advantage.
- To cause to happen or to occur as a consequence.
- To cause to work.
- To function correctly; to act as intended; to achieve the goal designed for.
- To influence.
- To effect by gradual degrees; as, to work into the earth.
- To move in an agitated manner.
- To behave in a certain way when handled
- (with two objects) To cause (someone) to feel (something); to do unto somebody (something, whether good or bad).
- To hurt; to ache.
- That is or are functioning.
- That suffices but requires additional work.
- In paid employment.
- Of or relating to employment.
- Enough to allow one to use something.
- Used in real life; practical.