Call otolaryngology department, having gaping lips (7)
I believe the answer is:
ringent
'gaping lips' is the definition.
'ringent' can be an answer for 'gaping' (thesaurus). I'm not sure about the 'lips' bit.
'call otolaryngology department' is the wordplay.
'call' becomes 'ring' (telephone call).
'otolaryngology department' becomes 'ent' (I am not sure about this - if you are sure you should believe this answer much more).
'ring'+'ent'='RINGENT'
'having' acts as a link.
Can you help me to learn more?
(Another definition for ringent that I've seen is " wide open".)