The most common and most likely answer to this crossword clue is the 4 letter word JILL
J
I
L
L
More clues leading to the result JILL
- Girl unwell after onset of jaundice
- With Jack poorly she appears?
- Character also falling sick after Jack?
- Prospective water carrier, quarter-pint, she said
- 1 down with Jack, in a bad way
- Female coming to harm with Jack
- Jack’s partner is unwell after taking some juice
- Jack’s friend Juliet gets sick
- She joins Jack climbing nursery slopes
Buddy explains!

The straight part
We know that "Jack’s partner" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case jack’s partner = jill.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 JILL mean?
JILL verb- (of a female) To masturbate.
- A female ferret.