This is the 3804th most frequent Swedish word.
jäkla
"Jäkla" is a mild swear word in Swedish, meaning "damn" or "bloody."
Here, 'jäkla' is used as an intensifier to convey the speaker's frustration or emphasis about the day.
Vilken jäkla dag det har varit!
What a darn day it has been!
In this sentence, 'jäkla' expresses annoyance towards the key or the situation of not finding it.
Jag kan inte hitta den där jäkla nyckeln.
I can't find that darn key.
The word 'jäkla' here reinforces the difficulty of the task described, adding emphasis to the statement.