It forms all or part of: annex; annexation; connect; connection; denouement; net (n.) "netting, network, mesh used for capturing;" nettle; nexus; node; nodule; noose.
It is the hypothetical source of/evidence for its existence is provided by: Sanskrit nahyati "binds, ties;" Latin nodus "knot;" Old Irish nascim "I bind, oblige;" Old English net "netting, network."
Middle English anelen, from Old English onælan "to set on fire, kindle; inspire, incite," from on- "on" (see an- (1)) + ælan "to burn, bake," from Proto-Germanic *ailan, "probably" [Watkins] from the same PIE root meaning "to burn" that is the source of ash (n.1). It is related to Old English æled "fire, firebrand," Old Norse eldr, Danish ild "fire."
The -n- was doubled after c. 1600 by analogy of Latinate words (annex, etc.; compare accursed, afford, allay). Meaning "to treat by heating and gradually cooling" (of glass, earthenware, metals, etc., to toughen them) was in late Old English. Related: Annealed; annealing.
1610s, "that which is added;" 1620s, "union" (now obsolete); 1630s, "action of adding to the end or adding a smaller to a greater," from Medieval Latin annexiationem (nominative annexatio) "action of annexing," noun of action from past-participle stem of annexare "to bind to," from ad "to" (see ad-) + nectere "to tie, bind" (from PIE root *ned- "to bind, tie"). The Middle English noun form was annexion "union; joining; territory acquired" (mid-15c.).