At first glance the passageway appears to be a mere crack or slit rising high in the seam between walls.

French windows opened a mere crack.

Therefore keep your lens shields down, except perhaps for the merest crack to see through, and, above all, don't move a millimeter, no matter what happens.

He saw the end of the chasm, a mere crack against the moonlight.

He had opened it only the merest crack.

Now these were no longer mere cracks in a surface; these were islands between gaps.

The window was open the merest crack, yet somebody was inside the room.

A mere crack separated the jamb from the door, and he put his left ear to the crack to listen.

It opened a mere crack, and Okiku made to slip inside, when a large hand dropped onto her shoulder.

He opened the door the merest crack and a bright glare of sunlight entered.