Frowning, have to admit (3)
I believe the answer is:
own
'admit' is the definition.
(own can mean to admit or acknowledge)
'frowning have' is the wordplay.
'have' indicates the answer is hidden within the clue.
'OWN' is hidden in the letters of 'frowning'.
'to' acts as a link.
(Other definitions for own that I've seen before include "Possess - recognise - admit" , "Acknowledge" , "Posses" , "Control" , "Personal; possess" .)