Titan unfortunately shrouds side of Tethys (5)
I believe the answer is:
atlas
'titan' is the definition.
(Atlas is an example)
'unfortunately shrouds side of tethys' is the wordplay.
'unfortunately' becomes 'alas' ('alas' is used to express regret).
'shrouds' indicates putting letters inside (shrouds can mean covers or contains).
'side of' indicates taking the first letters (the letter from one side of the word).
The initial letter of 'tethys' is 't'.
'alas' going around 't' is 'ATLAS'.
(Other definitions for atlas that I've seen before include "Segment of spine" , "Chart book" , "Book of geography" , "Collection of maps" , "collected world records?" .)