The most common and most likely answer to this crossword clue is the 6 letter word CASSIS
I've seen this crossword clue in The Guardian
C
A
S
S
I
S
More clues leading to the result CASSIS
- Cordial, if not exactly sororal?
- Hotel’s out of the base maybe for a sidecar — fruit syrup
- Accountant’s sibling’s blackcurrant cordial
- Liquor drunk by domestic assistant
- Cordial hospital not in the frame
- Russian Commonwealth welcomes idiot in syrup
- Caught help stealing last of liqueur
- Twit is after cold drink
- In neighbourhood of Italian town I tossed off fruit drink
- Sticky blackcurrant juice tonic as sister prescribes
Buddy explains!

The straight part
We know that "Cordial" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case cordial = cassis.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 CASSIS mean?
CASSIS noun- The blackcurrant plant, Ribes nigrum; the flavor of its berries
- A liqueur made from these berries, especially crème de cassis.
- (chiefly US) A wine flavor note, suggesting the fruity and full-bodied characteristics of the fruit; mostly referred to as simply blackcurrant in the UK, where the fruit is common.