adverb
indiscreetly; thoughtlessly; carelessly; frivolously
Adverb used to describe acting without due care or seriousness, often in a rash or frivolous manner. Typically appears as 軽々に.
軽々に約束してはいけない。
You must not make promises thoughtlessly.
彼は軽々に秘密を漏らした。
He carelessly let the secret slip.
軽々しい is an i-adjective meaning 'thoughtless' or 'indiscreet', often used to describe a person's character or actions, whereas 軽々 is a more formal, adverbial form.
Reduplication of 軽 (けい, 'light, frivolous'), forming an adverb meaning 'lightly, carelessly'. The exact historical derivation is uncertain, but the form is attested in classical Japanese.