The most common and most likely answer to this crossword clue is the 8 letter word VARIABLE
V
A
R
I
A
B
L
E
More clues leading to the result VARIABLE
- Feasible being without a room at first for changing
- Algebraic quantity that may work to contain two bits of arithmetic
- Changing sound to captivate rising artist
- Shifting sound keeps artist up
- Unsteady on nets after losing heart
- Unstable British settling east of drowned valley, in another valley
- Practicable involving annual return capable of change
- Having the capacity to live without a drop of refreshing fluid
- It might be of great, little, or even no value
- Wavering, likely to survive crossing a river
Buddy explains!

The straight part
We know that "fluid" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case fluid = variable.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 VARIABLE mean?
VARIABLE noun- Something that is variable.
- Something whose value may be dictated or discovered.
- A quantity that may assume any one of a set of values.
- A symbol representing a variable.
- A named memory location in which a program can store intermediate results and from which it can read them.
- A variable star.
- A shifting wind, or one that varies in force.
- (in the plural) Those parts of the sea where a steady wind is not expected, especially the parts between the trade-wind belts.
- Able to vary or be varied.
- Likely to vary.
- Marked by diversity or difference.
- Having no fixed quantitative value.
- Tending to deviate from a normal or recognized type.