Tea-set mug I designed is only approximate (10)

I believe the answer is:

guestimate

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

'only approximate' is the definition.
I can't tell whether this defines the answer.

'tea-set mug i designed' is the wordplay.
'designed' is an anagram indicator (designed with the letters).
'tea'+'set'+'mug'+'i'='teasetmugi'
'teasetmugi' with letters rearranged gives 'GUESTIMATE'.

'is' is the link.

Can you help me to learn more?

(Other definitions for guestimate that I've seen before include "Assessment" , "Rough value" , "Rough judgment" , "Result of rough calculation" , "rough idea" .)

I've seen this clue in the Sydney Morning Herald.

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.