Feel and be strangely weak (6)
I believe the answer is:
feeble
'weak' is the definition.
(similar in meaning)
'feel and be strangely' is the wordplay.
'and' says to put letters next to each other.
'strangely' indicates an anagram.
'feel'+'be'='feelbe'
'feelbe' anagrammed gives 'FEEBLE'.
(Other definitions for feeble that I've seen before include "Physically weak or lacking effectiveness" , "Weak, debilitated" , "Lacking force" , "Lacking strength or vigour" , "Weak - unconvincing" .)