Crossword Genius

A number of old pants on guy, and all fail! (4,2,6)

Ross

I believe the answer is:

lily of laguna

I'm a little stuck... Click here to teach me more about this clue!

'a number of old' is the definition.
I know nothing about this answer so I cannot judge whether this works.

'pants on guy and all fail' is the wordplay.
'pants' is an anagram indicator (UK informal term for 'nonsense' or 'rubbish').
'and' says to put letters next to each other.
'on'+'guy'+'all'+'fail'='onguyallfail'
'onguyallfail' is an anagram of 'LILY OF LAGUNA'.

Can you help me to learn more?

I've seen this clue in The Guardian.
Want a hint initially instead of a full solution? Install my app