The question says
When the square of a certain number is diminished by 5 times..
What does diminished by mean?
reduced.
Actually, there is a link to the parts of a subtraction problem. In words, we have
minuend
- subtrahend
----------------
difference
That is, the minuend is diminished by the amount subtracted (the subtrahend), yielding the difference.
*sigh* it seems folks have lost the ability to just pick up a dictionary any more ... It would have been much faster than posting such a question and waiting for any replies.