16 letters
- radiographically31
- radiotelephonies24
- rechoreographing31
- rechromatographs31
- rechromatography33
- rhynchocephalian36
- roentgenographic30
- semipornographic33
- sphygmomanometer35
- sphygmomanometry37
- stenographically31
- stereophonically29
- superenciphering32
- superphenomenons31
- thrombophlebitis33
- triphenylmethane31
- ultrasonographer26
- ultrasonographic29
- underemphasizing39
- unsophistication27