Train of thought of husband during walk (6)
I believe the answer is:
thread
'train of thought' is the definition.
(as in following the thread)
'husband during walk' is the wordplay.
'husband' becomes 'h'.
'during' is an insertion indicator.
'walk' becomes 'tread' (treading is a kind of walking).
'h' put into 'tread' is 'THREAD'.
'of' acts as a link.
(Other definitions for thread that I've seen before include "Twine" , "'Strand of cotton, silk etc (6)'" , "Dearth of stitching material" , "Fine strand" , "Thin yarn" .)