Taoiseach scratches aches, a bit (4)

I believe the answer is:

iota

I'm a little stuck... Click here to teach me more about this clue!

'bit' is the definition.
(I've seen this in another clue)

I don't understand how the rest of the clue works.

(Other definitions for iota that I've seen before include "Greek equivalent of the letter I" , "Greek letter; tiny amount" , "Scintilla" , "'Very small amount, jot (4)'" , "letter from abroad" .)

I've seen this clue in the Irish Times (Crosaire) and The Irish Times.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.