The phrase "a top knot" is correct and usable in written English.
It can be used to describe a hairstyle where the hair is gathered and tied up on the top of the head.
Example: "She styled her hair into a top knot for the formal event, giving her a chic and elegant look."
Alternatives: "a bun" or "a hair knot".
With a top knot and purposeful brows, she proffered a doll and a painted wooden cross.
New stems produce a distinctive fan of leaves known as a top knot.
An uncompromising hair style – a top knot so large it resembled a loaf of soda bread – finished off the silhouette.
A bisected strawberry crowned the concoction in much the same way that a top knot garnished the server's pate.
Cute blonde with a top knot and big brown purse has read halfway through Atlas Shrugged.
When I rang the bell, the man who answered the door was in flowing robes, with a top knot of hair.
For the shoot Kardashian West wears a custom made dress, a cluster of pearl necklaces and earrings by Mikimoto, vintage black satin gloves and a top-knot hairdo.
His appearance had always been immaculate but now he stood there with a full beard and his newly-long hair tied up in a top-knot.
With his "white beard and white hair tied up in a top-knot", and his talk of herbs and tinctures and his constant "spouting" of Latin verses, "Doctor Vlad" sends a ripple of suspicion through the small community.
In a central seat sits an upright young man in a pair of sail-like, calf-length black cotton trousers, his head of tightly drawn hair crowned with a top-knot finished in traditional Japanese style.
There is no little heroism in the fact that the Oxfordshire five-piece can come to giant sheds like these and sell them out with their jazz-tinged electronic rock, sung in falsetto by a nervy mendicant type sporting a beard and a top-knot.
