Bus fills in a very happy way (8)

I believe the answer is:

blissful

I'm a little stuck... Click here to teach me more about this clue!

'in a very happy way' is the definition.
I can't tell whether this defines the answer.

'bus fills' is the wordplay.
'bus fills' anagrams to 'BLISSFUL'.
But, I'm not clear how the anagram is indicated.

Can you help me to learn more?

(Other definitions for blissful that I've seen before include "Extremely happy" , "Completely happy and contented" , "Delighted" , "Joyous, rapt" , "Full of joy" .)

I've seen this clue in The Irish News.

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