define myexec ( $param = $name ) {

  exec { $name :
      cwd => "/tmp"
    , path => "/bin"
    , command => "/bin/echo ${name} ${param}"
  }

}

myexec{ "myexecname" : }
myexec{ "myexecnamewparam" : param => "givenparam" }

 puppet --debug ./TestNameInDefine.pp
debug: Creating default schedules
debug: Failed to load library 'shadow' for feature 'libshadow'
debug: //Myexec[myexecnamewparam]/Exec[myexecnamewparam]: Changing returns
debug: //Myexec[myexecnamewparam]/Exec[myexecnamewparam]: 1 change(s)
debug: //Myexec[myexecnamewparam]/Exec[myexecnamewparam]: Executing '/bin/echo myexecnamewparam givenparam'
debug: Executing '/bin/echo myexecnamewparam givenparam'
notice: //Myexec[myexecnamewparam]/Exec[myexecnamewparam]/returns: executed successfully
debug: //Myexec[myexecname]/Exec[myexecname]: Changing returns
debug: //Myexec[myexecname]/Exec[myexecname]: 1 change(s)
debug: //Myexec[myexecname]/Exec[myexecname]: Executing '/bin/echo myexecname '
debug: Executing '/bin/echo myexecname '
notice: //Myexec[myexecname]/Exec[myexecname]/returns: executed successfully
debug: Finishing transaction -609237778 with 2 changes