Under FreeBSD’s xterm the following setting made vim delete the last word after pressing ctrl+← (“Control+Backspace”):
set backspace=indent,eol,start
inoremap <C-?> <C-W>
cnoremap <C-?> <C-W>
For whatever reason after the last system upgrade this does not work anymore. Instead it results in vim inserting ^? into the document.
It works as expected if vim is used inside of screen.
Note:
- Pressing ctrl+v,ctrl+? in vim under xterm inserts 
^[[27;6;63~. - Pressing ctrl+v,ctrl+? in vim under screen inserts 
^?. 
vim --version gives:
VIM - Vi IMproved 8.1 (2018 May 18, compiled Nov 24 2019 15:10:11)
Included patches: 1-2237
Compiled by root@120amd64-default-job-19
Huge version with GTK3 GUI.  Features included (+) or not (-):
+acl               -farsi             +mouse_sysmouse    -tag_any_white
+arabic            +file_in_path      +mouse_urxvt       -tcl
+autocmd           +find_in_path      +mouse_xterm       +termguicolors
+autochdir         +float             +multi_byte        +terminal
-autoservername    +folding           +multi_lang        +terminfo
+balloon_eval      -footer            -mzscheme          +termresponse
+balloon_eval_term +fork()            +netbeans_intg     +textobjects
+browse            +gettext           +num64             +textprop
++builtin_terms    -hangul_input      +packages          +timers
+byte_offset       +iconv             +path_extra        +title
+channel           +insert_expand     +perl              +toolbar
+cindent           +job               +persistent_undo   +user_commands
+clientserver      +jumplist          +postscript        +vartabs
+clipboard         +keymap            +printer           +vertsplit
+cmdline_compl     +lambda            +profile           +virtualedit
+cmdline_hist      +langmap           -python            +visual
+cmdline_info      +libcall           +python3           +visualextra
+comments          +linebreak         +quickfix          +viminfo
+conceal           +lispindent        +reltime           +vreplace
+cryptv            +listcmds          +rightleft         +wildignore
+cscope            +localmap          +ruby              +wildmenu
+cursorbind        -lua               +scrollbind        +windows
+cursorshape       +menu              +signs             +writebackup
+dialog_con_gui    +mksession         +smartindent       +X11
+diff              +modify_fname      -sound             -xfontset
+digraphs          +mouse             +spell             +xim
+dnd               +mouseshape        +startuptime       +xpm
-ebcdic            +mouse_dec         +statusline        +xsmp_interact
+emacs_tags        -mouse_gpm         -sun_workshop      +xterm_clipboard
+eval              -mouse_jsbterm     +syntax            -xterm_save
+ex_extra          +mouse_netterm     +tag_binary        
+extra_search      +mouse_sgr         -tag_old_static    
Any ideas how to fix this, so that ctrl+← in vim deletes the last word?