Modes
company-dabbrev
is related to dabbrev: Dynamic abbreviations.
Summary
dabbrev-expand is essentially a form of completion where you first type a couple of letters of a word and press M-/ . When enabled in org mode it shows suggestions to complete a word.
Details
ref: https://jblevins.org/log/dabbrev-expand Emacs tries to complete the word by first looking at all the words in the current buffer, then in all other open buffers. Pressing M-/ multiple times will cycle through all possible completions.