What does the cryptic crossword clue "Einstein an egghead, not entirely silly (5)" mean?

The definition is "silly". The wordplay uses a hidden word. Hidden in "einsteIN AN Egghead, not entirely silly" The answer is Inane.

Einstein an egghead, not entirely silly (5)

Telegraph Prize Cryptic #3061 | 24 Down | 2020-06-21 flower