unshakeable
Word family
Synonym discussion
Sense: adjective/1
All four words describe a quality of being strong and not easily changed, but they differ in scope and tone. 'Firm' is the most general and informal — you can have a firm handshake, a firm decision, or firm beliefs. 'Steadfast' carries a warmer, more literary tone, often implying loyalty to a person or cause over many years. 'Unwavering' is very close to 'unshakeable' in meaning and intensity, focusing on a direction or line that does not bend. 'Resolute' is more about determined action in the face of difficulty — a resolute person makes a decision and sticks to it. For describing a lasting inner quality like trust or faith, 'unshakeable' and 'unwavering' are the strongest choices; 'firm' works but sounds weaker, while 'steadfast' adds a sense of devotion over time.
Common collocations
Etymology
Formed in English from the prefix 'un-' (meaning 'not') added to 'shakeable', which comes from the Old English verb 'sceacan' (to shake or move rapidly). The word has been used since the 1600s to describe things — first physical objects, later feelings and beliefs — that cannot be made to shake or waver.