The most common and most likely answer to this crossword clue is the 10 letter word STRAIGHTER
I've seen this crossword clue in The Guardian
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More clues leading to the result STRAIGHTER
Buddy explains!

The straight part
We know that "more respectable" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case more respectable = straighter.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 STRAIGHTER mean?
STRAIGHTER adjective- Not crooked or bent; having a constant direction throughout its length.
- (of a path, trajectory, etc.) Direct, undeviating.
- Perfectly horizontal or vertical; not diagonal or oblique.
- Describing the bat as held so as not to incline to either side; on, or near a line running between the two wickets.
- Direct in communication; unevasive, straightforward.
- Free from dishonesty; honest, law-abiding.
- Serious rather than comedic.
- In proper order; as it should be.
- In a row, in unbroken sequence; consecutive.
- Describing the sets in a match of which the winner did not lose a single set.
- Making no exceptions or deviations in one's support of the organization and candidates of a political party.
- Containing the names of all the regularly nominated candidates of a party and no others.
- Conventional, mainstream, socially acceptable.
- Heterosexual, attracted to people of the opposite sex.
- (of a romantic or sexual relation) Occurring between people of opposite sex.
- Not using alcohol, drugs, etc.
- Not plus size; thin.
- Strait; narrow.
- Stretched out; fully extended.
- Thorough; utter; unqualified.
- Of spirits: undiluted, unmixed; neat.
- Concerning the property allowing the parallel-transport of vectors along a course that keeps tangent vectors remain tangent vectors throughout that course (a course which is straight, a straight curve, is a geodesic).
- A cigarette, particularly one containing tobacco instead of marijuana. Also straight.