Vibration from the East is current hail (4,4)
I believe the answer is:
sine wave
'vibration' is the definition.
The definition and answer can be both related to natural events as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'from the east is current hail' is the wordplay.
'from the east' shows that the letters should be reversed in order (on a map from right to left).
'current' becomes 'new' (associated in meaning).
'hail' becomes 'ave' (greeting in Latin).
'is' backwards is 'si'.
'si'+'new'+'ave'='SINE WAVE'
Can you help me to learn more?
(Another definition for sine wave that I've seen is " Curved form".)