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hard; solid; tough
stiff; tight; wooden; unpolished (e.g. writing)
strong; firm (not viscous or easily moved)
safe; steady; honest; steadfast
obstinate; stubborn
bookish; formal; stuffy
昨日買ったこのパンはちょっと固いですね。
This bread is hard, isn't it?
親友と固い約束を交わして別れた。
We made a firm promise.
このパンは固くて食べにくいです。
This bread is hard and difficult to eat.