This is the 11259th most frequent Polish word.
głowa
Head.
The word 'głowa' is used here in its literal meaning to denote the head of an animal.
Mój pies ma bardzo dużą głowę.
My dog has a very big head.
'Głowa' here represents the metaphorical concept of the mind or space for thought.
Nie mogę przestać o tym myśleć, wciąż wraca mi to do głowy.
I can't stop thinking about it; it keeps coming back into my head.
In this context, 'głowa' refers idiomatically to a state of mental calmness or freedom from worry.