Hour of anticipation: Glaswegian singer to turn up and screech (7)
I believe the answer is:
ululate
'screech' is the definition.
(thesaurus)
'hour of anticipation glaswegian singer to turn up' is the wordplay.
'hour of anticipation' becomes 'eta' (expected time of arrival).
'glaswegian singer' becomes 'lulu' ().
'to turn up' says the letters should be written backwards.
'eta'+'lulu'='etalulu'
'etalulu' in reverse letter order is 'ULULATE'.
'and' acts as a link.
(Other definitions for ululate that I've seen before include "Howl loudly" , "Wail in grief" , "Give a hoot" , "Howl, wail, screech" , "Keen" .)