The most common and most likely answer to this crossword clue is the 5 letter word ANNEX
I've seen this crossword clue in The Guardian
A
N
N
E
X
More clues leading to the result ANNEX
- Join a former partner collecting news
- Seize a former partner, reportedly
- Appropriate planting kiss on Queen
- Join woman on Times
- Female getting vote is appropriate
- Knights go in swinging axe and conquer
- Something added on the end of affectionate princess’s letter?
- Appropriate queen given kiss
- Appropriate planting kiss on Queen?
- Take possession of girl with kiss
Buddy explains!

The straight part
We know that "conquer" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case conquer = annex.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 ANNEX mean?
ANNEX noun- An addition, an extension.
- An appendix to a book or document.
- An addition or extension to a building.
- An addition to the territory of a country or state, from a neighbouring country or state, normally by military force.
- To add something to another thing, especially territory; to incorporate.
- To attach or connect, as a consequence, condition, etc.
- To join; to be united.