Question: Is Wahi (Divine revelation) sent only to the Prophets by God Almighty? If so, then what does the following verse signify?

And your Lord has sent Wahi towards the honey bee... (16:68)

    Answer: The word Wahi has a literal meaning and is also used as a term. It is used in the literal meaning (to put something in the mind) in the verse you have referred to. As a term, it is used in the Qur’an at many instances as you very well know. When used as a term, it means religious guidance provided by the Almighty to His messengers.
    So one must try to determine when a word is used literally and when it is used as a term. Such variation in usage is very customary for many other Arabic words as well. Take the case of the word Zakah for example. As a term, it means a prescribed amount given in the way of Allah to obtain purity of heart and to obtain the blessings of Allah. Literally speaking, however, the word Zakah, in Arabic, has two meanings: ‘purity’ and ‘growth’. The words ‘purify them’ in the first and ‘people who will increase their wealth’ in the second verse of the Qur’an quoted below indicate these two meanings of the word:

Take alms from their wealth [O Prophet!] in order to cleanse them and purify them with it. (9:103)

And that which you give as loan on interest in order that it may increase on other people’s wealth has no increase with Allah; but that which you give as Zakah, seeking Allah’s countenance, it is these people who will increase their wealth [in the Hereafter]. (30:39)

    In other words, in these two verses, the word Zakah is used in its two literal meanings and not used as a term.
    So one must appreciate that all words that become terms are never stripped of their original literal meaning. The real thing is that one must be able to distinguish the difference in such usage. Consulting a good commentary or some scholar could always be of help on such occasions.