Turning up at one clutching love letter from Greece (4)
I believe the answer is:
iota
'letter from greece' is the definition.
(letter from the Greek alphabet)
'turning up at one clutching love' is the wordplay.
'turning up' says the letters should be written in reverse.
'one' becomes 'i' (Roman numeral).
'clutching' is an insertion indicator.
'love' becomes 'o' (love means zero in tennis).
'at'+'i'='ati'
'ati' placed around 'o' is 'atoi'.
'atoi' in reverse letter order is 'IOTA'.
(Other definitions for iota that I've seen before include "Old letter" , "Jot or tittle" , "Trace" , "Greek equivalent of the letter I" , "little part" .)