In the beginning, second wave of really dangerous, terrible floods came, threatening suspension (5,2,8)
I believe the answer is:
sword of damocles
'threatening suspension' is the definition.
(sword suspended in the Bible)
'in the beginning second wave of really dangerous terrible floods came' is the wordplay.
'in the beginning' suggests taking the first letters.
'really dangerous' becomes 'rd' (this might be a standard abbreviation which I don't know about).
'terrible' indicates an anagram.
The initial letters of 'second wave of' is 'swo'.
'floods'+'came'='floodscame'
'floodscame' is an anagram of 'ofdamocles'.
'swo'+'rd'+'ofdamocles'='SWORD OF DAMOCLES'
(Other definitions for sword of damocles that I've seen before include "It was perilously poised overhead" , "Impending threat" , "Imminently impending peril, disaster" , "imminent threat" , "precarious situation" .)