IPA: /ˈtwɛlvˌmʌnθ/
KK: /ˈtwɛlvˌmʌnθ/
A period of twelve months, which is equivalent to one year.
The project will take a twelvemonth to complete.
Twelvemonth is formed from "twelve" (from Old English "twelf", meaning the number 12) and "month" (from Old English "mōnaþ", meaning a lunar month). The word "twelvemonth" refers to a period of twelve months, or one year.
Think of the number 'twelve' and the word 'month' to remember that 'twelvemonth' means a full year, which is made up of twelve months.
No commonly confused words.