Greeting or calling out to someone, or (when referring to weather) frozen rain falling from the sky.
From Old English 'hægel' (hail/storm), from Germanic origins, related to the greeting 'hail' which meant 'be whole/healthy.' The two meanings merged in the concept of calling out.
The greeting 'hail' originally meant 'be whole/healthy'—so when Vikings said 'hail' to each other, they were essentially wishing each other good health; the frozen precipitation is a completely different word that sounds identical.
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