In "Bereft" by Frost, what do the words "wind" in the first line and "Word" in the two last lines refer to ?
I don't think there is any reason why we should take these words to mean anything other than the literal sense in which they are used in the poem. This poem describes the feelings of a speaker who appears to be "Bereft" by the passing of summer into the stormy fall weather. The "wind" of the first line therefore appears to refer to the autumn stormy winds that come, and in this poem stir up the leaves, making them "hiss" and causing them to "blindly strike" at the speaker's knee, turning nature into a violent form that is antagonistic towards the speaker.
Likewise, the "word" that is used three times at the end of the poem appears to refer to nothing more than the word or the message that the speaker is isolated, both in terms of being in his house alone, but also pointing towards his larger emotional and psychological isolation:
Word I was in the house alone
Somehow must have gotten abroad,
Word I was in my life alone,
Word I had no one left but God.
The "Word" is therefore that this speaker is alone, both physically, but also mentally and religiously, as he struggles with feeling bereft from someone or something as the seasons map out and enact his feelings of desolation.