Disaster as large taxi reverses into river (7)
I believe the answer is:
debacle
'disaster' is the definition.
(synonyms)
'large taxi reverses into river' is the wordplay.
'large' becomes 'L' (eg in clothes sizes).
'taxi' becomes 'cab' (synonyms).
'reverses' shows that the letters should be reversed in order.
'into' indicates putting letters inside.
'river' becomes 'dee' (River Dee).
'l'+'cab'='lcab'
'lcab' in reverse letter order is 'bacl'.
'bacl' placed into 'dee' is 'DEBACLE'.
'as' is the link.
(Other definitions for debacle that I've seen before include "Humiliating disaster" , "A sound defeat" , "foul-up" , "A complete collapse or messy failure" , "Sudden and violent collapse" .)