Romantic poet William Wordsworth uses synonyms in the first stanza to emphasize the singularity of the "Highland Lass" the speaker spies in a field. He uses the words "single," "solitary," "alone" and the phrase "by herself" to describe her situation of being on her own.
In the second stanza, the poet uses words and phrases that are antonyms to emphasize the beauty of the lass's singing. A "chaunt," "notes," and a "voice" oppose the use of the word "silence."
There are both similarities and contrasts in the third stanza. The synonyms "plaintive, "unhappy" "sorrow," "loss" and "pain" contrast with the antonyms "long ago" and "to-day" as the speaker speculates on the meaning of the girl's song.
In the final stanza, the speaker uses opposing ideas again. The speaker first listens "motionless and still," and then recalls he "mounted up the hill," denoting movement. He remembers the music that he can no longer hear.