The most common and most likely answer to this crossword clue is the 9 plus 6 letter word SHRINKING VIOLET
I've seen this crossword clue in Independent
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More clues leading to the result SHRINKING VIOLET
- One reluctant to be seen thinking lover is untrue
- Madly in love with Romeo, knight is one unwilling to make the first move?
- Wallflower flower flower
- One who’s withdrawn from contract, one wrongly given lot
- Wallflower becoming less wild, lacking nitrogen
- Mouse in short evil, badly nipping man
- Shy girl dressed in silk overnight
- One shy man with instrument in temple, tense
- Timid sort sadly given toil when faced by psychiatrist
- Who’s an introvert — Viole.. Viol...Vio ...?
Buddy explains!

The straight part
We know that "one unwilling to make the first move?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one unwilling to make the first move? = shrinking violet.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.