If you aren't sure which of two possible spellings is right, you can use the spell command with no arguments to find out. Type the name of the command, followed by a RETURN, then type the alternative spellings you are considering. Press CTRL-d (on a line by itself) to end the list. The spell command will echo back the word(s) in the list that it considers to be in error:
spell misspelling mispelling[CTRL-d] mispelling
If you're using, you need to add the -l option, since ispell doesn't read from standard input by default. (Even -l doesn't let ispell read from a pipe. The purpose of this option is to let you type in a list of words, just as shown above for spell; when you end the list, ispell will echo back the misspelled word, just like spell. There's no additional functionality there, except that ispell will use its local dictionaries and improved spelling rules.)
An even better way to do the same thing may be with . With just one argument, look searches the system word file, /usr/dict/words, for words starting with the characters in that one argument. That's a good way to check spelling or find a related word:
look helphelp helpful helpmate
look uses its -df options automatically when it searches the word list. -d ignores any character that isn't a letter, number, space or tab; -f treats uppercase and lowercase letters the same.