The Collaborative International Dictionary of English v.0.48:

Tunnel \Tun"nel\, v. t. [imp. & p. p. Tunneled
   (t[u^]n"n[e^]ld) or Tunnelled; p. pr. & vb. n. Tunneling
   or Tunnelling.]
   [1913 Webster]
   1. To form into a tunnel, or funnel, or to form like a
      tunnel; as, to tunnel fibrous plants into nests. --Derham.
      [1913 Webster]

   2. To catch in a tunnel net.
      [1913 Webster]

   3. To make an opening, or a passageway, through or under; as,
      to tunnel a mountain; to tunnel a river.
      [1913 Webster]

The Free On-line Dictionary of Computing (30 December 2018):

tunnelling

    (US: "tunneling") A networking technique used to
   carry data encoded in one protocol, A, over a channel using
   another protocol, B.  Protocol A is said to be "encapsulated" in
   protocol B and treats B as though it were a data link layer.
   Tunnelling is used to get data between administrative domains
   which use a protocol that is not supported by the internet
   connecting those domains.

   A historical example would be transmitting written text via Morse
   code - instead of having someone carry the text on paper, it is
   converted to (or encapsulated as) Morse code at one end and
   converted back to written text at the other.

   A more recent example would be tunnelling IPv6 over an IPv4
   network that does not support IPv6 natively.  Tunnelling
   techniques such as 6to4 or 6rd are used to encapsulate IPv6
   in the absence of native dual-stack support.

   (2013-10-07)