Touch head of freshwater fish (4)
I believe the answer is:
feel
'touch' is the definition.
(feeling is a kind of touching)
'head of freshwater fish' is the wordplay.
'head of' says to take the initial letters.
'fish' becomes 'eel' (eel is a kind of fish**).
The initial letter of 'freshwater' is 'f'.
'f'+'eel'='FEEL'
(Other definitions for feel that I've seen before include "Be aware of - texture" , "Instinct" , "Consider" , "Have a belief; touch" , "Perceive by touch" .)