The most common and most likely answer to this crossword clue is the 3 letter word SON
I've seen this crossword clue in The Times
S
O
N
More clues leading to the result SON
- Child, second, performing
- Part of issue paper's spoken of
- Relative of swan confused with lion
- Family member working in US city in southwest
- Close relative’s unfinished vocal piece
- Boy's piece of music, unfinished
- A child is born every second
- Issue often associated with Lumière
- Family member tabloid caught in the act?
- Tinned olive, not as it happens native?
Buddy explains!

The straight part
We know that "Part of issue" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case part of issue = son.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 SON mean?
SON noun- One's male offspring.
- A male adopted person in relation to his adoptive parents.
- A male person who has such a close relationship with an older or otherwise more authoritative person that he can be regarded as a son of the other person.
- A male person considered to have been significantly shaped by some external influence.
- A male descendant.
- A familiar address to a male person from an older or otherwise more authoritative person.
- An informal address to a friend or person of equal authority.
- To produce (i.e. bear, father, beget) a son.
- To address (someone) as "son".