Learner's definition of WEAK
[also more weak; most weak]
1 : having little physical power or ability : not strong
He has a weak throwing arm.
The illness left her too weak to stand up.
The child was born with weak lungs.
2 : having little power or force 3 : likely to break or stop working properly : not able to handle weight, pressure, or strain
4 a : having little power or influence b : not able to make good decisions or deal with difficult situations 5 a : lacking enough or the usual amount of an important ingredient
b : not powerful in action or effect
This tea is weak. [=it has little tea flavor]
weak cocktails [=cocktails that contain less than the usual amount of alcohol]
a weak bleach solution [=a mixture of water and a small amount of bleach]
6 : not likely to persuade or convince people that something is true, real, correct, etc.
Her arguments in support of the theory were weak.
He gave a weak excuse for being late.
The prosecution has a weak case.
7 : not having enough skill or ability 8 : failing to produce the result that is wanted : not effective
The pun was a weak attempt at humor.
The novel's plot was weak. [=it did not make sense, did not seem realistic, etc.]
9 : showing little confidence or enthusiasm 10 a : having a value that is small or is not increasing : less valuable b : in a poor financial condition 12 : smaller than the usual size 13 grammar : following the normal patterns by which the past tenses of verbs are usually formed : regular
the spirit is willing but the flesh is weak
weak at/in the knees
: so nervous or powerfully affected that it is difficult for you to stand weak is a general word that can describe either a temporary or permanent lack of strength. feeble stresses the kind of very great weakness that often makes other people feel pity or sympathy. frail is usually used to describe a very weak person who is easily injured especially because of illness or age.