On"slaught` (?), n. [OE. on on + slaught, slaht, slaughter. See Slaughter.]
1.
An attack; an onset; esp., a furious or murderous attack or assault.
By storm and onslaught to proceed.
Hudibras.
2.
A bloody fray or battle.
[Scot.]
Jamieson.
© Webster 1913.