Gather admission of stupidity (5)
I believe the answer is:
amass
'gather' is the definition.
(synonyms)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for amass that I've seen before include "Accumulate, pile up" , "Gathers" , "run up?" , "Be a compiler" , "Stockpile" .)