What does the cryptic crossword clue "What produces growth in pupil, slow but incomplete (7)" mean?

The definition is "What produces growth in pupil". The wordplay uses a deletion. DILATOR (deletion) = DILATOR The answer is DILATOR.

What produces growth in pupil, slow but incomplete (7)

Times Cryptic #28785 | 27 Across | 2023-12-13 flower