The phrase "a rather sinister" is correct and usable in written English.
It can be used to describe something that has an ominous or threatening quality.
Example: "The abandoned house had a rather sinister appearance, with its broken windows and overgrown garden."
Alternatives: "somewhat menacing" or "fairly ominous."
It would not be difficult to see, were one looking for such things, a rather sinister agenda in all this.
In the completed film Tom Hanks was able to portray six characters, from a train conductor to a rather sinister Santa Claus.
A rather sinister dinner guest proposes to his host a contest: if he identifies the wine the host is pouring, he wins the hand of the host's daughter.
As Riall pushes her hypothesis to the limit, Garibaldi emerges as a rather sinister figure, for whom absolutely everything was an opportunity for spin.
Delphine's closest girlhood friend, a rather sinister female undertaker, gets involved in a sordid subplot so poorly developed that it seems entirely extraneous to the book.
The music was intended as a way of calming us down, but thinking about it there's a rather sinister, Big Brother aspect to it all.
One – a rather sinister-looking early 20th-century medicine bottle – contained a lined sheet of paper.
They exist in a ménage in which the serenity of comforting routine is forever under siege, in part from forces incarnated by a blundering repair man (Magnus Jakobsson) and a hypnotic, rather sinister singer (Maria Sendow).
There is also a wonderfully seedy, coarse Tomsky from Gregory Dahl, and a contained, rather sinister Yeletsky from Nicholas Pallesen, while Alden turns Paulina, Lisa's confidante (sung by Catherine Young), into a vamp, the good time who's had by all.
The meshed hoods have an eerie and rather sinister appearance once put over the head of their targets.
A display is devoted to Sadie, a local ventriloquist's rather sinister model (as they always do seem to be) from the middle of the last century.
