What does the cryptic crossword clue "Prison leading famous people to develop pseudonyms (3,5)" mean?

The wordplay uses a charade (building blocks). PEN (synonym="prison") + NAMES (synonym="famous people") = PENNAMES The answer is PENNAMES.

Prison leading famous people to develop pseudonyms (3,5)

Guardian Cryptic #29600 | 15 Down | 2025-01-24 flower