Answer:

TIT

Answer	Crossword Clue
TIT	... for tat
TIT	Boob
TIT	Small songbird

TIT	"... -Willow": "The Mikado" song
TIT	Tat offset
TIT	.. for tat
TIT	Chickadee's cousin
TIT	.. for tat (h)
TIT	Chickadee relative
TIT	Little bird
TIT	Bearded ..: small bird

TIT	Little songbird
TIT	Palindromic bird
TIT	Retaliation for a tat?
TIT	Palindromic songbird
TIT	Tat equivalent
TIT	Palindromic little bird
TIT	Short-billed songbird
TIT	"...-Willow" ("Mikado" song)

TIT	Exchange for tat
TIT	Proverbial retribution
TIT	Chickadee cousin
TIT	Proverbial payback
TIT	"...a little tom-..-sang..."
TIT	Trade for tat
TIT	Small bird
TIT	Tiny songbird

TIT	Retaliation, so to speak
TIT	Retribution, so to speak
TIT	Metaphorical payback
TIT	Great ... (bird with a glossy blue-black head)
TIT	Wren-... (small brown bird)
TIT	Shrike ... (Australian bird)
TIT	Bearded ... (reedling)
TIT	Lead-in for lark or mouse

TIT	Small horse.
TIT	Suicidal hero of Ko-Ko's song
TIT	Small bird.
TIT	... willow.
TIT	Chickadee.