Help retired head of lyceum to make call (4)
I believe the answer is:
dial
'call' is the definition.
(thesaurus)
'help retired head of lyceum' is the wordplay.
'help' becomes 'aid' ('aid' can be a synonym of 'help').
'retired' is a reversal indicator.
'head of' suggests taking the first letters.
The first letter of 'lyceum' is 'l'.
'aid' in reverse letter order is 'dia'.
'dia'+'l'='DIAL'
'to make' acts as a link.
(Other definitions for dial that I've seen before include "Watch face" , "Clock face" , "Meter face" , "Ring the clock-face" , "Calibrated disc etc" .)