Chattering of the teeth; teeth clattering, typically from cold or fear.
寒さで歯がガチガチ鳴る。
My teeth are chattering from the cold.
怖くてガチガチと歯が震えた。
I was so scared that my teeth were chattering.
外で待っていたら寒さで口元がガチガチした。
Waiting outside made my mouth area chatter from the cold.
Stiff or rigid (physically), tense and contracted due to cold or anxiety.
彼は面接中、肩がガチガチに張っていた。
His shoulders were completely tense during the interview.
寒さで手がガチガチにこわばった。
My hands went stiff from the cold.
長時間の座り仕事で腰がガチガチになった。
Sitting for a long time made my lower back very stiff.
Rigid, inflexible (in personality or thinking); overly serious and not adaptable.
彼はルールにガチガチで、臨機応変に対応できない。
He's rigid about rules and can't respond flexibly.
あの上司はガチガチで話しにくい。
That boss is so rigid it's hard to talk to him.
ガチガチの考え方を変えるのは簡単ではない。
It's not easy to change a rigid way of thinking.
Relentlessly or intensely (e.g., working or studying) with no slack; thoroughly and without pause.
試験前は彼がガチガチに勉強していた。
Before the exam he was studying intensely.
締め切りが近くてチームがガチガチに働いた。
With the deadline approaching, the team worked flat out.
プロジェクトはガチガチにスケジュールが詰まっている。
The project schedule is packed tightly with no room to spare.