Answer:

abaa

Answer	Crossword Clue
ABAA	Last four lines of a villanelle, rhymewise
ABAA	Rhyme scheme at the end of a villanelle
ABAA	Rhyme scheme used in a villanelle

ABAA	Four-line rhyme scheme
ABAA	Simple rhyme scheme
ABAA	Quatrain rhyme scheme
ABAA	Quatrain rhyme scheme, maybe
ABAA	Rhyme scheme.
ABAA	Rhyme scheme
ABAA	Scheme for Frost
ABAA	Quatrain form

ABAA	Simple quatrain form
ABAA	Common quatrain form
ABAA	Rhyme pattern at the end of a villanelle
ABAA	Certain quatrain rhyme scheme
ABAA	Quatrain scheme, maybe
ABAA	Rhyme scheme of a villanelle's quatrain
ABAA	Rhyme scheme ending a villanelle
ABAA	Rhyme scheme in the last verse of a villanelle