Lieutenant in an oblique position in harbour (7)
I believe the answer is:
shelter
'harbour' is the definition.
(I know that harbour is a more specific form of the action shelter)
'lieutenant in an oblique position' is the wordplay.
'lieutenant' becomes 'lt' (abbreviation for lieutenant).
'in' means one lot of letters goes inside another.
'an oblique position' becomes 'sheer' (I am not sure about this - if you are sure you should believe this answer much more).
'lt' placed into 'sheer' is 'SHELTER'.
'in' is the link.
Can you help me to learn more?
(Other definitions for shelter that I've seen before include "retreat" , "Sanctuary; protect" , "Roof" , "Place giving protection" , "Shield as from rain" .)