Carefully consider (5)
(Other definitions for weigh that I've seen before include "Quantify mass" , "Find the heaviness of" , "Assess" , "Gauge" , "Put in the balance?" .)
'carefully consider' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for ponder that I've seen before include "Think deeply about, ruminate" , "Give thought to" , "Think weightily about" , "Carefully consider" , "Ruminate, mull over" .)