The phrase "altogether unusual" is correct and usable in written English.
It can be used to describe something that is completely or entirely out of the ordinary or expected.
Example: "The weather this winter has been altogether unusual, with temperatures soaring well above average."
Alternatives: "completely unusual" or "entirely uncommon".
The cohabitation is not altogether unusual.
It was, in many ways, not altogether unusual.
Such situations are not altogether unusual in sport.
It was a not altogether unusual predicament for this rapper, born Radric Davis, one of the most vigorous and exciting in recent memory.
The free concert on Tuesday — with Pace University as co-producer at its Michael Schimmel Center for the Arts, as part of the River to River festival — was altogether unusual.
4a305249-aebf-4a93-8c13-373794b9a115 BARCELONA, Spain — More than six million Americans live abroad, according to recent estimates, so it was not altogether unusual when the Ledermans, a family of four from California, moved here in 2011.
He first thought it was a labrador dog, but decided it was something altogether more unusual when he saw its tail was "about twice the length that a dog's would have been".
A second son avoided military service altogether - still unusual in this security-minded country - and lives in Paris.
So we need to keep an eye on your fruit intake and maybe eliminate fruits altogether if any unusual side effects occur, like anxiety over money, or anger over your spouse's infidelity.
For me, and most 20-something couples I know, the idea of waiting until marriage to have sex is unusual, if not altogether unheard-of.
These informative observations must however be viewed with some caution because transfection and site-directed mutagenesis may lead to more than a change in net charge as for example an altered molecular conformation, or altogether the introduction of an unusual claudin protein could lead to disturbance of strand organisation within native strands.
