The phrase "almost clandestine" is correct and usable in written English.
It can be used to describe something that is nearly secretive or hidden, but not entirely so.
Example: "The meeting was almost clandestine, held in a dimly lit room away from prying eyes."
Alternatives: "nearly secret" or "partially hidden".
They preoccupied him — these formless, almost clandestine memories.
Other outfits offer similar "pick-up" courses, though they remain relatively small and almost clandestine.
I rode the train past scrap metal yards, lonely lots and railroad tracks — the return seeming almost clandestine.
But these bare facts don't convey the almost clandestine excitement that surrounded the viewing and sharing of these precious objects.
"Some leave the country or escape to the south and live in an almost clandestine way for five years, waiting for their debts to clear".
Barred from public office in Florence as an insolvent debtor, Bernardo lived frugally, administering his small landed property near the city and supplementing his meagre income from it with earnings from the restricted and almost clandestine exercise of his profession.
On the other hand, the almost-clandestine ceremony might better reflect the tenuous nature of the "authority" the United States occupying forces had in the first place.
Atrocity photographs were scarce in the winter of 1936-37: the depiction of war's horrors in the photographs Woolf discusses in Three Guineas seemed almost like clandestine knowledge.
Cassettes and recordings circulated almost like samizdat, the clandestine publications that circumvented censorship.
In the same episode, Dawn, who has been stealing from stores, including Anya's magic shop, lies to Buffy and goes on a clandestine and almost deadly date.
But almost four years after the clandestine links between gem smugglers, warlords and gunrunners inspired threats of a consumer boycott of diamonds, this culminating moment seemed almost an anticlimax.
