This is the 5699th most frequent Swedish word.
haka
Chin.
In this sentence, 'haka' refers to 'chin', a physical part of the human body.
Han har en liten haka.
He has a small chin.
Here, 'haka' is part of the expression 'haka på', meaning 'to follow or tag along'.
Hon hänger alltid med på nya idéer och hakar på.
She always follows along with new ideas and tags along.
In this instance, 'haka' appears in 'haka upp dig', an idiomatic phrase meaning 'to get hung up or stuck on something'.