The term 'firstly' is used to describe something that happens FIRST or at the beginning of a process. It can be broken down into four crossword solutions: FIRST (5 letters), BASICALLY (9 letters), FUNDAMENTALLY (13 letters), and INITIALLY (9 letters). FIRST is an adverb meaning 'before anything else, ' while BASICALLY is an adverb meaning 'in essence.' FUNDAMENTALLY is an adverb meaning 'at the core, ' and INITIALLY is an adverb meaning 'at the start.' All four words are used to describe something that occurs FIRST in a sequence of events.