The most common and most likely answer to this crossword clue is the 15 letter word UNCOMMUNICATIVE
U
N
C
O
M
M
U
N
I
C
A
T
I
V
E
More clues leading to the result UNCOMMUNICATIVE
Buddy explains!
The straight part
We know that "Reserved" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case reserved = uncommunicative.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 UNCOMMUNICATIVE mean?
UNCOMMUNICATIVE adjective- Tending not to communicate; not communicating.