The only way one can do anything (5)
I believe the answer is:
alone
'the only' is the definition.
(thesaurus)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for alone that I've seen before include "Single" , "unique" , "Exclusively, by oneself" , "Without anybody or anything else" , "without partner?" .)