Tiny worker, one going round in circles (6,4)
I believe the answer is:
minute hand
'one going round in circles' is the definition.
(part of a clock)
'tiny worker' is the wordplay.
'tiny' becomes 'minute' (I've seen this before**).
'worker' becomes 'hand' (hand is a kind of worker).
'minute'+'hand'='MINUTE-HAND'
(Other definitions for minute hand that I've seen before include "Bit of a watch" , "is on time" , "Indicator that goes right round hourly" , "Part of watch or clock" , "that Mimi had" .)