Using all letters

                                                                           speechlessly

                                                                          The other words:

                                                                              cheesy

                                                                               cycle

                                                                              cycles

                                                                              eyeless

                                                                            helplessly

                                                                               hypes

                                                                               lycee

                                                                              lycees

                                                                              lychee

                                                                              lychees

                                                                               lyses

                                                                               peppy

                                                                               psych

                                                                              psyche

                                                                              psyches

                                                                              psychs

                                                                               seepy

                                                                              shelley

                                                                              shelly

                                                                               shyly

                                                                              sleepy

                                                                               slyly

                                                                               sylph

                                                                              sylphs

                                                                              sylphy

                                                                               yells

                                                                               yelps

                                                                               yeses

                                                                              yesses