Pouring down (7)
(Other definitions for teeming that I've seen before include "Chock-a-block" , "Alive" , "full of creatures?" , "Full of, abounding in" , "Swarming in to meeting" .)
'pouring down' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for raining that I've seen before include "Falling in drops" , "Showering" , "Pouring perhaps" , "Bad weather" , "Showery" .)