Poet's daughters penning lines with nurse (6)
I believe the answer is:
dryden
'poet's' is the definition.
(John Dryden)
'daughters penning lines with nurse' is the wordplay.
'daughters' becomes 'dd' (a genealogical abbreviation for daughter repeated).
'penning' means one lot of letters goes inside another.
'lines' becomes 'ry' (abbreviation for railway).
'with' means one lot of letters go next to another.
'nurse' becomes 'EN' (abbreviation for state-enrolled nurse).
'dd' placed around 'ry' is 'dryd'.
'dryd'+'en'='DRYDEN'
(Other definitions for dryden that I've seen before include "English poet, d. 1700" , "Charles II's Poet Laureate" , "John -, English seventeenth century poet, dramatist" , "playwright" , "17th century English poet and dramatist" .)