Documents can be spell-checked with the spell command. To see a list of all the words that the spellchecker doesn't recognize,
spell <documentname>
To spell-check a LATEX document, use the texspell command:
texspell <documentname.tex>
To check the spelling of a single word or group of words on the command line (instead of from a file), enter the spell command followed by a carriage return, then enter the word(s) followed by an eoln character, <ctrl-d>.