Generation seen in retreats every now and then (4)
I believe the answer is:
eras
'generation seen' is the definition.
I can't judge whether this definition defines the answer.
'retreats every now and then' is the wordplay.
'every now and then' means one should take alternating letters (letters selected at regular intervals).
The alternate letters of 'retreats' are 'ERAS'.
'in' acts as a link.
Can you help me to learn more?
(Other definitions for eras that I've seen before include "Periods of time" , "Long and distinct periods of history" , "Periods, ages" , "typeface" , "Epochs" .)