Hear thou the word of the Lord. The punishment of him who tried to impede God's message. Drop not thy word. Be not continually pouring forth prophecy. The word is used similarly in Micah 2:6, Micah 2:11 and Ezekiel 21:2.
The idea, though not the term, is taken from Deuteronomy 32:2. Septuagint, μὴ ὀχλαγωγήσῃς, "raise no tumult," which rather expresses Amaziah's fear of the effect of the utterance than translates the word.
St. Jerome's explanation is somewhat too subtle, "Stillare prophetas idioma Scripturarum est, quod non totam Dei simul inferant iram, sed parvas stillas comminatione denuntient."