Yen to tuck into ice-creams - source of some reticence (7)
I believe the answer is:
coyness
'reticence' is the definition.
(I have seen 'Arch reticence ' mean 'coyness' so perhaps 'reticence' could also mean 'coyness')
'yen to tuck into ice-creams source of some' is the wordplay.
'yen' becomes 'y'.
'to tuck into' is an insertion indicator.
'ice-creams' becomes 'cones' (ice-cream cones).
'source of' indicates taking the first letters.
The first letter of 'some' is 's'.
'y' put inside 'cones' is 'coynes'.
'coynes'+'s'='COYNESS'
(Other definitions for coyness that I've seen before include "Demureness" , "Affected modesty" , "evasive quality" , "Shyness" , "Pretended modesty" .)