The most common and most likely answer to this crossword clue is the 7 letter word SIBLING
I've seen this crossword clue in The Daily Telegraph
S
I
B
L
I
N
G
Buddy explains!
The straight part
We know that "Close relative" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case close relative = sibling.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 SIBLING mean?
SIBLING noun- A person who shares a parent; one's brother or sister who one shares a parent with.
- A node in a data structure that shares its parent with another node.
- The most closely related species, or one of several most closely species when none can be determined to be more closely related.