Rashness, n.
The quality of state of being rash. We offend . . . by rashness, which is an affirming or denying, before we have sufficiently informed ourselves. South.
Syn. -- Temerity; foolhardiness; precipitancy; precipitation; hastiness; indiscretion; heedlessness; inconsideration; carelessness. See Temerity.
Shades of meaning
Fernald has no entry of its own for rashness; he lists it under temerity.
Where he writes about it:
Rashness applies to the actual rushing into danger without counting the cost; temerity denotes the needless exposure of oneself to peril which is or might be clearly seen to be such. — from temerity
Rashness is used chiefly of bodily acts, temerity often of mental or social matters; there may be a noble rashness, but temerity is always used in a bad sense. — from temerity
Venturesomeness dallies on the edge of danger and experiments with it; foolhardiness rushes in for want of sense, heedlessness for want of attention, rashness for want of reflection, recklessness from disregard of consequences. — from temerity