The word I seek is split into letters,
each letter enclosed in a riddle below.
Each riddle will get harder as the number increases.
You know the length of my word, but what's the word?
One letter wrong is likely to change the whole word!
Letter #1:
At the cross roads,
there's a twist down one path
and dead ends the rest.
there's one of me on every line
Letter #2:
You will be female without me,
But if I come I will let you walk out of here alive
I split to make a number of relevance to me
Letter #3:
With me you are will gain wisdom
But if you think you know it all your eyes will never see knowledge
Don't ditch me - I am as good as two of you
Letter #4:
The English language just wouldn't be the same without me
In the name of Englishmen, I present them all
And lag behind to help them with their language
Letter #5:
I am cousin of the square, though he be twice as large as me
Though I got half the score of my friend 'I' in my degree°
Lover of me or loather of me, this oath is over
What word am I and what does each riddle mean?
EDIT
Seeing as no-one of yet has letter #2, I'll put some emphasis on it:
OLD
You will be female without me,
But if I come I will let you walk out of here alive
I split to make a number of relevance to me
NEW
You will be female without me,
But if I come I will let you walk out of here alive
I double to make a number of relevance to me
In a chart of chemistry