Spot daughter on tree (4)
I believe the answer is:
dash
'spot' is the definition.
(thesaurus)
'daughter on tree' is the wordplay.
'daughter' becomes 'd' (genealogical abbreviation).
'on' says to put letters next to each other (in a down clue, letters appear on others).
'tree' becomes 'ash' (ash is a kind of tree).
'd'+'ash'='DASH'
(Other definitions for dash that I've seen before include "quite mild oath" , "hasty journey" , "Short race run at top speed" , "Hurry ("must ____!")" , "Hurry; hyphen" .)