The most common and most likely answer to this crossword clue is the 8 letter word EMBATTLE
I've seen this crossword clue in Independent
E
M
B
A
T
T
L
E
More clues leading to the result EMBATTLE
- Let team bowled out prepare to get attacked
- English medic and old PM almost ready for fight
- Prepare for conflict, as doctor crashes into former PM when cycling
- Fortify English doctor and former PM briefly
- Let me go out, grab club and prepare for fight
- Fortify even parts of Reims before a town in the south
- Remembers central alliance finally left prime minister ready for war
- Call one out following poor BAME representation – prepare defence
- Old PM’s back seen first by doctor, to add strength
- Having melted away in club, lead dancer goes out to prepare for a fight
Buddy explains!

The straight part
We know that "prepare defence" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case prepare defence = embattle.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 EMBATTLE mean?
EMBATTLE verb- To arrange in order of battle; to array for battle
- To prepare or arm for battle; to equip as for battle.
- To be arrayed for battle.
- A merlon, or a single one of the series of solid projections of a battlement
- To furnish with battlements; give the form of battlements to