lengthen

1 ENTRIES FOUND:
lengthen /ˈlɛŋθən/ verb
lengthens; lengthened; lengthening
lengthen
/ˈlɛŋθən/
verb
lengthens; lengthened; lengthening
Britannica Dictionary definition of LENGTHEN
1 
[no object] : to become longer
2 
[+ object] : to make (something) longer
— opposite shorten