shallow thinking; imprudence; rashness
Refers to a lack of careful thought or foresight, often leading to hasty decisions. Used both as a noun and as a na-adjective.
I failed because of a rash decision.
quick temper; short temper
Describes a personality prone to anger or irritation over small things. Often used in the phrase 短慮な性格.
I'm always surprised by his imprudence.
He has a short temper and gets angry easily.
短慮 is a more literary term for shallow, short-sighted thinking, while 軽率 is the common word for rash behavior in everyday speech.
Compound of 短 (short, brief) and 慮 (consideration, thought). The exact historical derivation is uncertain, but the meaning follows naturally from the kanji components.