Boast about old star (5)
I believe the answer is:
garbo
'star' is the definition.
Both the definition and answer are singular nouns.
Perhaps they are linked in a way I don't understand?
'boast about old' is the wordplay.
'boast' becomes 'brag' (synonyms).
'about' is a reversal indicator.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'brag' in reverse letter order is 'garb'.
'garb'+'o'='GARBO'
Can you help me to learn more?
(Other definitions for garbo that I've seen before include "Swedish film actress Greta" , "Famous film actress" , "Reclusive film star" , "Greta -, Swed. actress" , "Swedish film star who wanted to be alone" .)