This is the 12790th most frequent Russian word.
крохотным
Tiny.
In this sentence, 'крохотный' is used as an adjective describing the size of the kitten as being very small.
Крохотный котёнок уснул на подушке.
The tiny kitten fell asleep on the pillow.
Here, 'крохотную' (a form of 'крохотный') modifies the noun 'трещину' to indicate the small size of the crack.
Она заметила крохотную трещину на стекле.
She noticed a tiny crack in the glass.
In this example, 'крохотной' describes the pen, emphasizing its extremely small size in relation to its usability.