The tiniest amount, ten thanks (4)
I believe the answer is:
iota
'the tiniest amount' is the definition.
'iota' can be an answer for 'amount' (iota is a kind of amount). I am not sure about the 'the tiniest' bit.
'ten thanks' is the wordplay.
'ten' becomes 'io' (IO resembles 10).
'thanks' becomes 'ta' (UK informal version of 'thank you').
'io'+'ta'='IOTA'
Can you help me to learn more?
(Other definitions for iota that I've seen before include "Ninth Greek character" , "Jot or tittle" , "Smidgen" , "The smallest possible amount, or the Greek i" , "Greek letter of little value" .)