Obviously more than one short day (5)
I believe the answer is:
month
'day' is the definition.
(thesaurus)
'obviously more than one short' is the wordplay.
'obviously more' becomes 'mon' (I can't justify this - if you can you should believe this answer much more).
'one' becomes 'an' (an apple is one apple).
'short' is a deletion indicator (short can mean missing or absent).
'than' with 'an' taken away is 'th'.
'mon'+'th'='MONTH'
Can you help me to learn more?
(Other definitions for month that I've seen before include "Eg, February" , "Division of year" , "One of 12 divisions" , "Four-week period" , "Lunation" .)