Hooked up, I see, with friend (6)

'hooked' is the definition.
(thesaurus)

'up i see with friend' is the wordplay.
'up' says the letters should be written in reverse (in down clue: letters go upwards).
'i see' becomes 'ah' (exclamation used to indicate understanding).
'with' means one lot of letters go next to another.
'friend' becomes 'mate' (mate is a kind of friend).
'ah' written backwards gives 'ha'.
'ha'+'mate'='HAMATE'