The most common and most likely answer to this crossword clue is the 6 letter word DEFINE
I've seen this crossword clue in The Guardian
D
E
F
I
N
E
More clues leading to the result DEFINE
- Exactly describe backward condition in deep valley
- Carefully determine what’s cooked in feed
- Explain when bit of fish found in river
- Accurately describe part of plane found in river
- Give a plain description of French capital
- River without end in Paris? Explain!
- Mark out empty Dundee ground
- Spell out letters at end of crossword clue, all right?
- Pin down characters next to each other in feast
- Characterise evidence of shark dwelling in river
Buddy explains!

The straight part
We know that "Carefully determine" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case carefully determine = define.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 DEFINE mean?
DEFINE noun- A kind of macro in source code that replaces one text string with another wherever it occurs.
- To determine with precision; to mark out with distinctness; to ascertain or exhibit clearly.
- To settle, decide (an argument etc.)
- To express the essential nature of something.
- To state the meaning of a word, phrase, sign, or symbol.
- To describe, explain, or make definite and clear; used to request the listener or other person to elaborate or explain more clearly his or her intended meaning of a word or expression.
- To demark sharply the outlines or limits of an area or concept.
- To establish the referent of a term or notation.