Took one's time boarding (5)
I believe the answer is:
stole
'took' is the definition.
(stealing is a kind of taking)
'one's time boarding' is the wordplay.
'one' becomes 'sole' (synonyms).
'time' becomes 't' (abbreviation).
'boarding' means one lot of letters goes inside another.
'sole' going around 't' is 'STOLE'.
(Other definitions for stole that I've seen before include "Took - scarf" , "Purloined the wide scarf" , "Long shawl" , "Item of clothing" , "Moved silently" .)