American sailor circling shore, by the way (7)
I believe the answer is:
apropos
'by the way' is the definition.
(French-derived term meaning 'by the way')
'american sailor circling shore' is the wordplay.
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'sailor' becomes 'os' (ordinary seaman).
'circling' means one lot of letters goes inside another (circling can mean going around or containing).
'shore' becomes 'prop' (I've seen this in another clue).
'a'+'os'='aos'
'aos' going around 'prop' is 'APROPOS'.
(Other definitions for apropos that I've seen before include "Poor sap, being to the point" , "On the subject of" , "Poor sap (anag) - to the purpose" , "Regarding" , "To the point, germane" .)