offhand
off + hand
https://gyazo.com/64a11cb7344a58c62bdd913811ab80bf
adjective
ungraciously or offensively nonchalant or cool in manner:
«…に対して» そっけない, 無愛想な «with»
e.g. his offhand way of talking.
adverb
without previous thought or consideration:
(よく調べないで)すぐに, 即答で
e.g. I can't think of a better answer offhand.