The most common and most likely answer to this crossword clue is the 7 letter word DOUBLED
I've seen this crossword clue in Financial Times
D
O
U
B
L
E
D
More clues leading to the result DOUBLED
Buddy explains!

The straight part
We know that "Copied/sound of -th in Welsh" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case copied/sound of -th in welsh = doubled.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 DOUBLED mean?
DOUBLED verb- To multiply by two.
- To fold over so as to make two folds.
- To be the double of; to exceed by twofold; to contain or be worth twice as much as.
- To increase by 100%, to become twice as large in size.
- To get a two-base hit.
- (sometimes followed by up) To clench (a fist).
- (often followed by together or up) To join or couple.
- To repeat exactly; copy.
- (often followed by as) To play a second part or serve a second role.
- To turn sharply, following a winding course.
- To sail around (a headland or other point).
- To duplicate (a part) either in unison or at the octave above or below it.
- (usually followed by "on") To be capable of performing (upon an additional instrument).
- To make a call that will double certain scoring points if the preceding bid becomes the contract.
- To double down.
- To cause (a ball) to rebound from a cushion before entering the pocket.
- (followed by for) To act as substitute.
- To go or march at twice the normal speed.
- To multiply the strength or effect of by two.
- To unite, as ranks or files, so as to form one from each two.
- (of a station) To transmit simultaneously on the same channel as another station, either unintentionally or deliberately, causing interference.