Louse egg in upturned container (3)
I believe the answer is:
nit
'louse egg' is the definition.
(I've seen this before)
'upturned container' is the wordplay.
'upturned' is a reversal indicator.
'container' becomes 'tin' (tin is a kind of container).
'tin' written backwards gives 'NIT'.
'in' acts as a link.
(Other definitions for nit that I've seen before include "Stupid person; egg" , "Muggins" , "Cause of much head-scratching" , "Egg of parasitic insect" , "small egg" .)