Cover for embarrassment when gaffe left one reeling (3,4)
I believe the answer is:
fig leaf
'cover for embarrassment' is the definition.
(fig leaves cover one's nudity)
'gaffe left one reeling' is the wordplay.
'left' becomes 'l' (common abbreviation).
'one' becomes 'i' (Roman numeral).
'reeling' indicates anagramming the letters.
'gaffe'+'l'+'i'='gaffeli'
'gaffeli' anagrammed gives 'FIG-LEAF'.
'when' acts as a link.
(Other definitions for fig leaf that I've seen before include "Adam and Eve attire" , "Greenery worn by Adam or Eve" , "It may be used to cover embarrassing nudity" , "Green growth from 17 Across to cover nudity" , "Covering for Adam's private parts" .)