Alexander Schmidt, Shakespeare Lexicon and Quotation Dictionary

Clamour, vb., to cry, to wail: “the obscure bird --ed the livelong night,” Mcb. II, 3, 65.
Strange expression: “'tis well they are whispering: c. your tongues, and not a word more,” Wint. IV, 4, 250.* Nares: 'An expression taken from bell-ringing; it is now contracted to clam, and in that form is common among ringers. The bells are said to be clammed, when, after a course of rounds or changes, they are all pulled off at once, and give a general crash or clam, by which the peal is concluded.' Dyce: 'Mr. Hunter observes that the same phrase occurs in Taylor the Waterpoet's Sir Gregory Nonsense: Cease friendly cutting throats, c. the promulgation of your tongues'. And Mr. Arrowsmith explains clamour to mean curb, restrain, considering it as equivalent to chaumbre or chammer (Fr. chommer), and cites the following passages from Udall's translation of the Apophthegms of Erasmus: 'For Critias menaced and threatened him, that unless he chaumbred his tongue in season etc. and: from no sort of men in the world did he refrain or chaumbre the taunting of his tongue.' -- It ought, after all, to be taken into account that in our passage it is the Clown that is speaking. If not a misprint, as Gifford supposed, it may be a misapplication of the word for 'charm.'