The most common and most likely answer to this crossword clue is the 7 letter word JUSTIFY
I've seen this crossword clue in The Times
J
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Buddy explains!
The straight part
We know that "To fit into line" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case to fit into line = justify.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 JUSTIFY mean?
JUSTIFY verb- To provide an acceptable explanation for.
- To be a good, acceptable reason for; warrant.
- To arrange (text) on a page or a computer screen such that the left and right ends of all lines within paragraphs are aligned.
- To absolve, and declare to be free of blame or sin.
- To give reasons for one’s actions; to make an argument to prove that one is in the right.
- To prove; to ratify; to confirm.
- To show (a person) to have had a sufficient legal reason for an act that has been made the subject of a charge or accusation.
- To qualify (oneself) as a surety by taking oath to the ownership of sufficient property.