An incomplete lock-up of military importance (3)
I believe the answer is:
col
'military importance' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.
'an incomplete lock-up' is the wordplay.
'an incomplete' means to remove the last letter.
'up' says the letters should be written backwards (in down clue: letters go upwards).
'lock' with its final letter taken off is 'loc'.
'loc' reversed gives 'COL'.
'of' acts as a link.
Can you help me to learn more?
(Other definitions for col that I've seen before include "Low point of saddle between two peaks" , "A depression in mountain range" , "Mustard" , "route through mountains" , "Somewhere up on the mountain" .)