Adding endings to words that end in a double ‘l’

In American English, adding endings such as –ment, –ful, or -ness to words that end in a double ‘l’ poses no spelling problems. You just add the endings to the basic word:
install    installment
skill       skillful
small     smallness
If you are adding –ly, though, you do need to drop the final ‘l’ before adding the ending:
chill       chilly
frill        frilly
In British English, the situation is different: words ending in double ‘l’ drop the final ‘l’ when the endings – ment or –ful are added:
install    instalment
skill        skilful
See also


Grammar and usage