Working with sailor, one heading to oxbow lake (7)
I believe the answer is:
ontario
'lake' is the definition.
(I know that Ontario is a lake)
'working with sailor one heading to oxbow' is the wordplay.
'working' becomes 'on' (e.g. a machine is working or on).
'with' says to put letters next to each other.
'sailor' becomes 'tar' (slang term for a sailor).
'one' becomes 'i' (Roman numeral).
'heading to' indicates taking the first letters (the head of the word).
The first letter of 'oxbow' is 'o'.
'on'+'tar'+'i'+'o'='ONTARIO'
(Other definitions for ontario that I've seen before include "One of the Great Lakes" , "A North American lake" , "one of the provinces" , "provincial area" , "part of Canada" .)