What is this ..., if full of care, we have no time to stand and stare?'' (Davies) (4)
I believe the answer is:
life
(Other definitions for life that I've seen before include "'While there's .... there's hope'" , "Actuarial estimate of our remaining years" , "Existence - biography" , "Baffin oiler (anag) - 7 film" , "Birth to death" .)