The DICT protocol serves word definitions over a simple text protocol on port 2628. You can query a public DICT server directly with curl, or install the dict client for a nicer interface.

curl dict://dict.org/d:linux             # raw protocol response
sudo dnf install dict                     # or apt-get install dict dict-wn
dict linux                                # cleaner formatted output
dict -d wn linux                          # a specific dictionary/database (e.g. WordNet)
dict -D                                   # list available databases on the server

Combine with cowsay for a novelty one-liner: dict linux | cowsay -n. Public DICT servers rate-limit and are not guaranteed to stay up; for scripted or offline use, a local dictionary database or a proper API-based service is more reliable.