Initially tied with ideal new English string (5)
I believe the answer is:
twine
'string' is the definition.
('twine' can be a synonym of 'string')
'initially tied with ideal new english' is the wordplay.
'initially' suggests taking the first letters.
'english' becomes 'e' (abbreviation).
The first letters of 'tied with ideal new' is 'twin'.
'twin'+'e'='TWINE'
(Other definitions for twine that I've seen before include "twist" , "Tough string" , "Coil" , "Strong thread or string" , "can get into knots" .)