Webster's Revised Unabridged Dictionary · 1913

handfast

handfast (hand"fȧst`) , noun

1.
Hold; grasp [Obsolete] — Shakespeare
2.
Custody; power of confining or keeping. [Obsolete] — Shakespeare
3.
A contract; specifically, an espousal. [Obsolete]

handfast , adjective

Fast by contract; betrothed by joining hands. [Obsolete] — Bale

handfast , transitive verb

1.
To pledge; to bind. [Obsolete]
2.
To betroth by joining hands, in order to permit cohabitation, before the formal celebration of marriage; in some parts of Scotland it was in effect to marry provisionally, permitting cohabitation for a year, after which the marriage could be formalized or dissolved. [Obsolete]

Handfasting was a simple contract of agreement under which cohabitation was permitted for a year, at the end of which time the contract could be either dissolved or made permanent by a formal marriage. Such marriages, at first probably not intended to be temporary, are supposed to have originated in Scotland from a scarcity of clergy, and to have existed at times in other countries.

handfast , adjective

[German handfest; hand hand + fest strong. See Fast.]

Strong; steadfast. [Rare] — Carlyle