Latch To A Grave

I am a Lord's attendant
A soldier's loyal kin
To my master dear
Companion to my king

A queen on me sometimes
Nobly, swears an oath

I hold in my possession
The latch to a grave

My tongue is firm
Yet oft I, to the poet
A loan of words
Give for his verse

Faultless is my form
And noble is my cause
Yet in the hands of some
Deathly is my touch