Little bit in and out, say, oddly (4)
I believe the answer is:
iota
'little' is the definition.
(thesaurus)
'bit in and out say oddly' is the wordplay.
'bit' says to take the initial letters (I've seen 'bits of' mean this).
'and' says to put letters next to each other.
'oddly' means one should take alternating letters (letters in odd-numbered positions).
The first letter of 'in' is 'i'.
'out'+'say'='outsay'
The alternating letters of 'outsay' are 'ota'.
'i'+'ota'='IOTA'
(Other definitions for iota that I've seen before include "Old letter" , "Gk. letter; tiny amount" , "Hint" , "Greek letter; tiny amount" , "Contrivance" .)