Complete partially typed words

Start typing a word, and then press M-/ to cycle through possible completions of the word based on words you have previously typed.

For an improved completions, add the following to your emacs config file (note this is done already if you are using my recommended setup, prelude).

;; use hippie-expand instead of dabbrev
(global-set-key (kbd "M-/") 'hippie-expand)