Small container caught by set of similar things initially overlooked (6)
I believe the answer is:
casket
'small container' is the definition.
'casket' can be an answer for 'container' (casket is a kind of container). I am unsure of the 'small' bit.
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for casket that I've seen before include "Small box or chest" , "Small box - coffin" , "Ornamental chest" , "Coffin or jewellery box" , "Small box for holding jewellery" .)