Cell entrance confining this writer (6)
I believe the answer is:
gamete
'cell' is the definition.
(I know that gamete is a type of germ cell)
'entrance confining this writer' is the wordplay.
'entrance' becomes 'gate' (type of entrance).
'confining' means one lot of letters goes inside another.
'this writer' becomes 'me' (the person who is writing these clues).
'gate' enclosing 'me' is 'GAMETE'.
(Other definitions for gamete that I've seen before include "An egg or sperm cell" , "something seedy?" , "Egg- or sperm-cell" , "Male or female germ cell" , "Cell which unites with another in reproduction to form a zygote" .)