Summer shirt (3)
'summer shirt' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for tee that I've seen before include "Starting peg" , "Golfer's support" , "Start of a hole in golf" , "Golfing support" , "support of leisure activity" .)
(Other definitions for tanktop that I've seen before include "turret?" , "Warm garment" .)