Touch upon a condition (4)

I believe the answer is:

abut

'touch upon' is the definition.
(I've seen this before)

'a condition' is the wordplay.
'condition' becomes 'but' (I've seen this in another clue).
'a'+'but'='ABUT'

(Other definitions for abut that I've seen before include "Touch upon" , "Lie adjacent to" , "Of building or land, end or lean against" , "Adjoin, border" , "Impinge" .)

I've seen this clue in the Sydney Morning Herald.

Want a hint initially instead of a full solution? Install my app