Maybe first troops call crossing north (7)
I believe the answer is:
ordinal
'maybe first' is the definition.
('first' is an ordinal number)
'troops call crossing north' is the wordplay.
'troops' becomes 'or' (military abbreviation for other ranks).
'call' becomes 'dial' (as in making a phone call).
'crossing' means one lot of letters goes inside another.
'north' becomes 'N' (abbreviation).
'dial' placed around 'n' is 'dinal'.
'or'+'dinal'='ORDINAL'
(Other definitions for ordinal that I've seen before include "Relating to series order" , "Possibly first or second" , "For example, first" , "Numerals such as first and second" , "Ninth, maybe" .)