The letter 'was couched in' polite terms.
a psychiatrist's 'couch'
(..) Oh horrible, oh horrible, most horrible. If thou hast nature in thee, bear it not Let not the royal bed of Denmark be a couch for luxury and damned incest But howsoever thou pursuest this act... ...taint not thy mind, nor let thy soul contrive against thy mother aught (..)2015 Hamlet