Used for the feeling when something falls short of expectations, or when a plan fails to produce the desired result.
Archaic use for something nonsensical or absurd. Not used in modern Japanese outside of historical contexts.
I got up early for nothing—the shop was closed and I was left disappointed.
The concert I was looking forward to was canceled; it was a real let-down.
I bought lottery tickets, but they were all blanks.
The shot missed the goal and ended up a failure.
In old documents, すか is sometimes used to mean 'nonsense'.
The plan I had been looking forward to ended in a disappointing failure.
I drew a lottery ticket, but I got another loser.
がっかり is the common adverb/する-verb for feeling let down, whereas すか is a noun naming the disappointing outcome itself.
The origin is uncertain. It may be related to the mimetic word すかっと (feeling refreshed or empty), but the exact derivation is unclear.