Party hat not for top dog? (5)
I believe the answer is:
alpha
'for top dog?' is the definition.
(I've seen this in another clue)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for alpha that I've seen before include "Beginning" , "starter" , "star outshining the others" , "very good rating" , "First-rate" .)