1. A system for disambiguating a text input of a sub-word of a long word on an electronic device, comprising: a virtual keyboard having a plurality of virtual keys; an input pointing device adapted for inputting the text input by the pointing device being placed on a key of the keyboard corresponding to the first character of the sub-word, and then by the input device being moved to subsequent keys corresponding to subsequent characters of the sub-word, so as to produce a trajectory pattern; a dictionary database associated with the keyboard and the pointing device, the dictionary database comprising words and associated frequencies of usage; a long word dictionary (LWD) derived from the dictionary database, having a smaller size than that of the dictionary database and configured according to an arrangement of the keys in the keyboard; and a partial trajectory recognition module associated with the keyboard and the pointing device, wherein the trajectory pattern is evaluated to produce sub-word solutions; wherein the sub-word solutions are used in conjunction with the LWD to selectively recognize at least one prediction solution corresponding to at least one long word.