"A girl friend, or
wife." If we're getting more urban with it, but it could apply to any friend, partner, helper etc. who would
maybe say the same about you, in an equally endearing but dominant gesture. "He's my second hand around here.", so it could be a Son on the farm who also knows how to run things, but has a boss, teacher or, as in this example, a
Father. There's an element of a derogatory nature potentially implied with this comment, but it's not a requirement, in it's usage. Speaking of which is probably dated.
Maybe it's usage has shifted that way over the years and run it's self out.
He's my second
hand around here. Without him I would struggle like I've only got one hand! Also young Johnny has a brand new "second hand", his
wife Jill, to
add to the family that support each other.