The most common and most likely answer to this crossword clue is the 5 letter word HAVEN
I've seen this crossword clue in The Daily Telegraph
H
A
V
E
N
More clues leading to the result HAVEN
- Own name used in safe location
- Consume last of open port
- Number trailing behind accept asylum
- Get heading for natural harbour
- Retreat inside with a vengeance
- Where to find peace, as man, woman, and children finally do
- Oasis embraced by chav endearingly
- Oasis or Nirvana dropping Ecstasy
- Not quite paradise, though sea-sick sailors might think so!
- Paradise lost — point to a safe place
Buddy explains!

The straight part
We know that "Oasis" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case oasis = haven.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 HAVEN mean?
HAVEN noun- A harbour or anchorage protected from the sea.
- (by extension) A place of safety; a refuge or sanctuary.
- (by extension) A peaceful place.
- To put into, or provide with a haven.