In its traditional sense, momentarily means for a moment, so momentarily would be synonymous with briefly, not with soon. But the word is often used to mean in a moment—synonymous with soon or shortly. This newer sense of momentarily is often derided by protectors of traditional English, but it is well established, especially in North America. Even there, however, the word is still usually used in its older sense.
It’s scary when a speeding puck strikes your neck, momentarily making it impossible to breathe. [Chicago Tribune]
Bailey said his vision momentarily went black but joked that his sunglasses saved him and he’ll be fine. [San Francisco Chronicle]
Gus is momentarily rattled but easily counters Hank by pointing out the spotty record-keeping in the Pinochet years. [AV Club]
The victim managed to get to his feet momentarily before again being punched to the ground. [Edinburgh Evening News]
As he chatted with his clients, his attention was momentarily diverted by news on a large video screen. [Calgary Herald]
Obstructive sleep apnoea (OSA) occurs when children with enlarged tonsils stop breathing momentarily throughout the night. [New Zealand Herald]