Mike across the pond in deficit (5)
I believe the answer is:
minus
'mike across the pond in deficit' is the definition.
I can't tell whether this defines the answer.
'mike across the pond in' is the wordplay.
'mike' becomes 'M' (phonetic alphabet: alpha, bravo, charlie etc.).
'across' is a charade indicator (letters next to each other) (across can mean on).
'the pond' becomes 'us' (I can't justify this - if you can you should believe this answer much more).
'us' after 'in' is 'inus'.
'm'+'inus'='MINUS'
Can you help me to learn more?
(Other definitions for minus that I've seen before include "Less, without" , "'Take away' sign" , "Lacking; negative" , "Take-away (sign)" , "Lacking; below zero" .)