The most common and most likely answer to this crossword clue is the 8 letter word CARDINAL
I've seen this crossword clue in The Guardian
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More clues leading to the result CARDINAL
Buddy explains!
The straight part
We know that "Red/ /key/ (8)" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case red/ /key/ (8) = cardinal.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 CARDINAL mean?
CARDINAL noun- One of the officials appointed by the pope in the Roman Catholic Church, ranking only below the pope and the patriarchs, constituting the special college which elects the pope. (See Wikipedia article on Catholic cardinals.)
- Any of a genus of songbirds of the finch family, Cardinalis.
- Any of various related passerine birds of the family Cardinalidae (See Wikipedia article on cardinals) and other similar birds that were once considered to be related.
- (color) A deep red color, somewhat less vivid than scarlet, the traditional colour of a Catholic cardinal's cassock. (same as cardinal red)
- Short for cardinal number, a number indicating quantity, or the size of a set (e.g., zero, one, two, three). (See Wikipedia article on Cardinal number.)
- (grammar) Short for cardinal numeral, a word used to represent a cardinal number.
- Short for cardinal flower (Lobelia cardinalis), a flowering plant.
- Short for cardinal tetra (Paracheirodon axelrodi), a freshwater fish.
- (bow) A woman's short cloak with a hood, originally made of scarlet cloth.
- Mulled red wine.
- Of fundamental importance; crucial, pivotal.
- Of or relating to the cardinal directions (north, south, east and west).
- Describing a "natural" number used to indicate quantity (e.g., zero, one, two, three), as opposed to an ordinal number indicating relative position.
- Having a bright red color (from the color of a Catholic cardinal's cassock).