What does the cryptic crossword clue "Intellect can be a depressing affair (4,6)" mean?

The wordplay uses a charade (building blocks). GREY (synonym="”depressing”") + MATTER (synonym="”affair”") = GREYMATTER The answer is GREYMATTER.

Intellect can be a depressing affair (4,6)

Guardian Cryptic #29519 | 8 Down | 2024-10-21 flower