Sailor taking part-time soldiers on river (3)
I believe the answer is:
tar
'sailor' is the definition.
(slang term for a sailor)
'part-time soldiers on river' is the wordplay.
'part-time soldiers' becomes 'ta' (abbreviation for Territorial Army. I am not sure about the 'part-time' bit.).
'on' is a charade indicator (letters next to each other) (in a down clue, letters appear on others).
'river' becomes 'r' (abbreviation).
'ta'+'r'='TAR'
'taking' is the link.
Can you help me to learn more?
(Other definitions for tar that I've seen before include "Road-making substance" , "Informal sailor, the rat" , "A sailor; a preservative" , "Informal sailor or coal distillation" , "Slang sailor or road surfacing material" .)