Nothing in it; a mere tittle (4)

I believe the answer is:

iota

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'mere tittle' is the definition.
'iota' can be an answer for 'tittle' (synonyms). I am unsure of the 'mere' bit.

'nothing in it a' is the wordplay.
'nothing' becomes 'O' (looks like zero - 0).
'in' means one lot of letters goes inside another.
'o' inserted into 'it' is 'iot'.
'iot'+'a'='IOTA'

Can you help me to learn more?

(Other definitions for iota that I've seen before include "Greek letter - small quantity" , "very small part" , "Ninthe letter of the Greek alphabet" , "Just a jot, from Greek alphabet" , "letter from abroad" .)

I've seen this clue in The Globe and Mail.

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