Moderate losing head on more than one occasion! (5)
I believe the answer is:
often
'on more than one occasion' is the definition.
(often means on regular occasions)
'moderate losing head' is the wordplay.
'moderate' becomes 'soften' (synonyms).
'losing head' means to remove the first letter.
'soften' with its first letter taken off is 'OFTEN'.
(Other definitions for often that I've seen before include "More than occasionally" , "Frequent" , "Perhaps daily" , "In many cases" , "Much of the time" .)