What does the cryptic crossword clue "Maximally exposed, first covering up hole (8)" mean?

The wordplay uses a container (one word inside another). LEAK (synonym="hole") in BEST (synonym="first") = BLEAKEST The answer is BLEAKEST.

Maximally exposed, first covering up hole (8)

Guardian Cryptic #29310 | 13 Across | 2024-02-20 flower