A bearing on time (4)
I believe the answer is:
aeon
'time' is the definition.
(aeon is a kind of time)
'a bearing on' is the wordplay.
'bearing' becomes 'e' (**).
'a'+'e'+'on'='AEON'
(Other definitions for aeon that I've seen before include "Very long and indefinite period of time" , "Immeasurably long period of time" , "Indefinitely long period of time" , "long term" , "Vast time period" .)