Showing pity for nothing: an empty hundred years, with no beginning and no end (2,4)
I believe the answer is:
oh dear
'hundred years with no beginning and no end' is the definition.
I know nothing about this answer so I cannot judge whether it can be defined by this definition.
'showing pity for nothing an empty' is the wordplay.
I cannot really understand how this works, but
'nothing' could be 'o' (looks like zero - 0) and 'o' is found within the answer.
'an' could be 'a' and 'a' is present in the answer.
'empty' could be 'e' (abbreviation e.g. on guages) and 'e' is located in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for oh dear that I've seen before include "That's disappointing!" , "alas" , "rueful remark" , "That's a shame" , "Cry of dismay" .)