Check:

• when the word is underlined in Word
• if you have noticed the word spelled differently elsewhere
• when similar words vary across your content
• if you are in any way unsure about the word.

Examples of spellings that commonly vary include:

• using z or s – such as -ize vs -ise
• using -re or -er – such as litre vs liter
• omitting u – such as color vs colour
• omitting a vowel from oe or ae – such as estrogen vs œstrogen vs oestrogen
• doubling consonants when adding an ending – such as labeled vs labelled
• dropping the last e when adding an ending – such as acknowledgement vs acknowledgment
• using -ed or -t for past tenses – such as spelt vs spelled
• using -ices or -ixes for plurals – such as appendices vs appendixes
• using -ae or -s for plurals – such as formulae vs formulas
• using -ic or -ical (in cases where the meaning is the same), such as botanic vs botanical.