The term “carbuncle” can clue a crossword in two common senses: a skin condition or a gemstone. Here are the likely answers based on typical crossword word lengths and clue styles.

• If the clue is about a skin ailment: CARBUNCLE often refers to a deep bacterial skin infection. A common 6–9 letter answer that fits many crosswords is STAPH or BOIL, with BOIL being a shorter and frequent synonym for a single lesion. For a more precise fit, consider the length given in the puzzle.
• If the clue is about a gemstone: CARBUNCLE historically denotes a red garnet or a red gemstone. A 7-letter gemstone-related answer could GARNET.

Common synonyms you might see:

• For the skin condition sense: BOIL, FURUNCLE (more technical, 8 letters), CARBUNCLE (the word itself in some clues).
• For the gemstone sense: GARNET, CARBUNCLE (when used as a gemstone name in older clues).

If you share the exact clue text and the puzzle’s word length, the number of letters, and any intersecting letters you already have, I can pinpoint the most likely answer.