For fear that (4)
'for fear that' is the definition.
(synonyms)
This is the entire clue.
(Other definitions for lest that I've seen before include "For fear that (something happens)" , "In order not to, say forget?" , "In order not to, to avoid the risk that" , "To avoid the risk that - we forget?" , "For fear that (something should happen)" .)
(Other definitions for most that I've seen before include "Almost all" , "Greatest in amount or degree" , "Nearly all, majority" , "In the highest degree" , "Extremely, very" .)