'Weak-kneed' definitions:

Definition of 'weak-kneed'

(from WordNet)
adjective
Lacking will power or resolution; "the role of the dissenter is not for the weak-kneed"

Definition of 'Weak-kneed'

From: GCIDE
  • Weak-kneed \Weak"-kneed`\, a. Having weak knees; hence, easily yielding; wanting resolution. --H. James. [1913 Webster]