*Imminent (7)
'imminent' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for pending that I've seen before include "Not yet seen to" , "Awaiting settlement" , "Awaiting action" , "undecided" , "near" .)
(Other definitions for horizon that I've seen before include "Where earth meets sky" , "Earth/sky interface" , "Line where sky meets sea" , "Oz rhino (anag)" , "viewed distantly" .)