Feel and be strangely weak (6)
I believe the answer is:
feeble
'weak' is the definition.
(I know that weak can be written as feeble)
'feel and be strangely' is the wordplay.
'and' means one lot of letters go next to another.
'strangely' indicates an anagram.
'feel' put after 'be' is 'befeel'.
'befeel' is an anagram of '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" .)