Iron perhaps introduced into otherwise square meal (9)
I believe the answer is:
elevenses
'iron perhaps introduced into otherwise square meal' is the definition.
I can't tell whether this defines the answer.
'iron perhaps introduced into otherwise square' is the wordplay.
'iron perhaps' becomes 'even' (I've seen this before. I am not sure about the 'perhaps' bit.).
'introduced into' is an insertion indicator.
'otherwise' becomes 'else' (synonyms).
'square' becomes 's' (abbreviation).
'even' going into 'else' is 'elevense'.
'elevense'+'s'='ELEVENSES'
Can you help me to learn more?
(Other definitions for elevenses that I've seen before include "tenses found immediately before this?" , "energy getting second break" , "Morning refreshment break" , "Mid-morning refreshment" , "Mid-morning snacks" .)