The word that is similar in meaning to the word, 'remarkable' is:

'Remarkable' means worthy of attention, striking, or extraordinary. 'Astonishing' similarly means surprising or amazing — both convey the sense of something noteworthy or impressive. 'Remedial' means corrective, 'remaining' means left over, and 'optional' means not compulsory. None of these are synonyms of 'remarkable.' Astonishing best matches the meaning.