The most common and most likely answer to this crossword clue is the 4 letter word BABY
I've seen this crossword clue in Independent
B
A
B
Y
More clues leading to the result BABY
- Very young child born in creek
- Infant born in space near window?
- Very small book-lined alcove
- Young bird's heading into tree
- Brown horse bearing black foal, say
- Graduate alongside infant
- Minds children in small sections crossing gorge briefly
- Infant born during recess
- Honey bee caught in inlet
- & 4 & 7 … this 9, by loading First Class up with whizz next to hold
Buddy explains!

The straight part
We know that "this 9 (PE No1)" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case this 9 (pe no1) = baby.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 BABY mean?
BABY noun- A very young human, particularly from birth to a couple of years old or until walking is fully mastered.
- Any very young animal, especially a vertebrate; many species have specific names for their babies, such as kittens for the babies of cats, puppies for the babies of dogs, and chickens for the babies of birds. See for more.
- Unborn young; a fetus.
- A person who is immature, infantile or feeble.
- A person who is new to or inexperienced in something.
- The lastborn of a family; the youngest sibling, irrespective of age.
- A term of endearment used to refer to or address one's girlfriend, boyfriend or spouse.
- A form of address to a man or a woman considered to be attractive.
- A pet project or responsibility.
- An affectionate term for anything.
- A small image of an infant; a doll.
- To coddle; to pamper somebody like an infant.
- To tend (something) with care; to be overly attentive to (something), fuss over.
- Of a child: very young; of the age when he or she would be termed a baby or infant.
- Of an animal: young.
- Intended for babies.
- (of vegetables, etc.) Picked when small and immature (as in baby corn, baby potatoes).