We are short, or used to be (4)
I believe the answer is:
were
This clue might be a double definition.
'we are' is the first definition.
(contraction of 'we are')
'used to be' is the second definition.
(eg 'you were...' means 'you used to be...')
'short or' is the link.
I am not very happy about this link. Some or all of it may belong to one of the definitions.
Can you help me to learn more?
(Other definitions for were that I've seen before include "(We/you) existed" , "Lycanthrope" , "'Are, in the past (4)'" , "Used to be" , "Existed in the past" .)