Garland wrote in invisible ink (3)
I believe the answer is:
lei
'garland' is the definition.
('lei' can be a synonym of 'garland')
'wrote in invisible ink' is the wordplay.
'wrote in' indicates the answer is hidden within the clue (I've seen 'written in' mean this).
'LEI' is hidden within 'invisible ink'.
(Other definitions for lei that I've seen before include "Hawaiian necklace of flowers" , "Honolulu chain of flowers" , "Floral garland" , "Flower garland of Hawaii" , "Band of flowers" .)