What does the cryptic crossword clue "Partial fraction (in theory)? (5)" mean?

The wordplay uses a hidden word. Hidden in fractioN IN THeory Edit: thanks to Roz @90 for explaining that this clue is &lit The answer is NINTH.

Partial fraction (in theory)? (5)

Guardian Cryptic #29407 | 29 Across | 2024-06-12 flower