The Collaborative International Dictionary of English v.0.48:

Twofold \Two"fold`\, a. [Cf. Twifold.]
   Double; duplicate; multiplied by two; as, a twofold nature; a
   twofold sense; a twofold argument.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Twofold \Two"fold`\, adv.
   In a double degree; doubly.
   [1913 Webster]

WordNet (r) 3.0 (2006):

twofold
    adv 1: by a factor of two; "the price increased twofold last
           year" [syn: twofold, two times]
    adj 1: having more than one decidedly dissimilar aspects or
           qualities; "a double (or dual) role for an actor"; "the
           office of a clergyman is twofold; public preaching and
           private influence"- R.W.Emerson; "every episode has its
           double and treble meaning"-Frederick Harrison [syn:
           double, dual, twofold, two-fold, treble,
           threefold, three-fold]
    2: twice as great or many; "ate a double portion"; "the dose is
       doubled"; "a twofold increase" [syn: double, doubled,
       twofold, two-fold]

Moby Thesaurus II by Grady Ward, 1.0:

40 Moby Thesaurus words for "twofold":
   Janus-like, ambidextrous, as much again, bifacial, bifold, biform,
   bilateral, binary, binate, biparous, bivalent, conduplicate,
   disomatous, double, double-barreled, double-faced, doubly, dual,
   dualistic, dually, duple, duplex, duplicate, dyadic, geminate,
   geminated, paired, second, secondary, twice, twice as much,
   twice over, twin, twinned, two times, two-faced, two-level,
   two-ply, two-sided, two-story