Tiny tot swallowing a bit of a snub (6)
I believe the answer is:
minute
'tiny' is the definition.
(minute can mean small)
'tot swallowing a bit of a snub' is the wordplay.
'tot' becomes 'mite' (both can mean a young child).
'swallowing' indicates putting letters inside.
'a bit of a snub' becomes 'nu' (I can't justify this - if you can you should give a lot more credence to this answer).
'mite' placed around 'nu' is 'MINUTE'.
Can you help me to learn more?
(Other definitions for minute that I've seen before include "Measure of time" , "microscopic" , "Tiny - proportion of time" , "It's not very long" , "Barely perceptible" .)