Fallopian tube traveler (4)
I believe the answer is:
ovum
'fallopian tube traveler' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for ovum that I've seen before include "Female gamete" , "Reproductive cell, 'egg' in Latin" , "Female reproductive cell" , "bit of life potentially" , "A female egg-cell" .)