An onomatopoeic word for a sharp clacking sound (e.g., footsteps) or used adverbially to mean 'just barely' or 'living with no margin'.
下駄の鼻緒が切れて、カツカツと変な音がした。
The thong of the geta broke and there was a strange clacking sound.
今月は出費が多くて、生活がカツカツだ。
I have a lot of expenses this month, so life is really tight.
彼はいつも時間にカツカツで、余裕がない。
He's always cutting it close on time and has no leeway.