Answer:
Hither is one of a set of three adverbs which are all about directionality. They correspond to three words which are about location: where, here and there. If an object is located near the speaker, it is "here"; if it is further away, it is "there", and if we don't know its location we have an interrogative "where". If something is in motion but it is headed towards "here" it is coming hither; if it is headed towards "there", it is going thither, and if we need to know in what direction it is going, we ask whither it is going. Please note that the three prefixes h-, th- and wh- have the same relation to each other whether the ending is -ere or -ither.
Use of these words has declined over the years, probably because we are able to get the information we need from the verb used without the delicate distinction which these words represent.
Shakespeare uses all of these, and frequently. In Romeo and Juliet, Romeo asks "A fair assembly: whither should they come?" In Othello, the Duke says "Fetch Desdemona hither" "Conduct me thither" says the Princess in Love's Labour's lost.