The most common and most likely answer to this crossword clue is the 10 letter word ACCEPTANCE
I've seen this crossword clue in The Daily Telegraph
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More clues leading to the result ACCEPTANCE
Buddy explains!
The straight part
We know that "favourable reaction" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case favourable reaction = acceptance.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 ACCEPTANCE mean?
ACCEPTANCE noun- The act of accepting; a receiving of something offered, with acquiescence, approbation, or satisfaction; especially, favourable reception; approval.
- Belief in something; agreement, assent.
- The state of being accepted.
- The usual or accepted meaning of a word or expression.
- An assent and engagement by the person on whom a bill of exchange is drawn, to pay it when due according to the terms of the acceptance; the bill of exchange itself when accepted.
- An agreeing to the action, proposals, or terms of another by some act which results in the conclusion of a legally binding contract; the reception or taking of a thing bought as that for which it was bought, or as that agreed to be delivered, or the taking of possession of a thing as owner.
- The act of an authorized representative of the government by which the government assents to ownership of existing and identified supplies, or approves specific services rendered, as partial or complete performance of a contract.
- A list of horses accepted as starters in a race.
- A conserved property of the light in an optical system which characterizes how "spread out" the light is in terms of angle and area: it is the product of its cross-sectional area (normal to the direction of propagation) and the solid angle it subtends.