For instance, could be past being nervous (5)
I believe the answer is:
tense
'nervous' is the definition.
(similar in meaning)
'for instance could be past being' is the wordplay.
I cannot quite see how this works, but
'being' could be 'ens' (philosophical term for being or existence) and 'ens' is present in the answer.
The remaining letters 'te' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for tense that I've seen before include "Drawn" , "Rigid, or grammatical time" , "Maybe past" , "Anxious, nervous" , "in the past, perhaps" .)