Letters that make top-up
o, p, t, u are letters that make 'top-up'
1 possible definitions for 'top-up'
Under this definition, top-up is a noun and has the following properties:
'top-up' can be a type of indefinite quantity.
'top-up' can be a region of United Kingdom, UK, U.K., Britain, United Kingdom of Great Britain and Northern Ireland, Great Britain